AI Trajectory

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "KMSANReasoning": "",
  "NeedsKMSAN": false,
  "Reasoning": "The patch modifies pci_do_resource_release_and_resize() in drivers/pci/setup-bus.c, which handles PCIe Resizable BAR (REBAR) reconfiguration. This function is only invoked during probe of physical discrete GPUs (amdgpu, i915, xe) or via the sysfs resource\u003cN\u003e_resize attribute. The sysfs attribute and the underlying helper are only accessible for devices advertising the PCIe Resizable BAR extended capability (PCI_EXT_CAP_ID_REBAR or PCI_EXT_CAP_ID_VF_REBAR), which requires physical PCIe hardware (e.g., discrete GPUs) and is not implemented or emulated by any virtual device in standard virtualized fuzzing environments (QEMU / GCE). Consequently, the modified code is structurally unreachable for syzkaller.",
  "WorthFuzzing": false
}

null

{
  "PatchDiff": "commit c8c5fa29195aaa5aab551f0f9a459dd7c4fb8a00\nAuthor: syz-cluster \u003ctriage@syzkaller.com\u003e\nDate:   Wed Sep 16 01:50:50 2026 +0000\n\n    syz-cluster: applied patch under review\n\ndiff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c\nindex e8c94aa1d3c12..ed16ef7c26fa7 100644\n--- a/drivers/pci/setup-bus.c\n+++ b/drivers/pci/setup-bus.c\n@@ -2380,6 +2380,7 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size\n \tstruct resource *res = pci_resource_n(pdev, resno);\n \tstruct pci_dev_resource *dev_res;\n \tstruct pci_bus *bus = pdev-\u003ebus;\n+\tstruct pci_dev *bridge = pci_upstream_bridge(pdev);\n \tstruct resource *b_win, *r;\n \tLIST_HEAD(saved);\n \tunsigned int i;\n@@ -2397,6 +2398,8 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size\n \tif (ret)\n \t\treturn ret;\n \n+\tdown_read(\u0026pci_bus_sem);\n+\n \tpci_dev_for_each_resource(pdev, r, i) {\n \t\tif (i \u003e= PCI_BRIDGE_RESOURCES)\n \t\t\tbreak;\n@@ -2415,13 +2418,21 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size\n \n \tpci_resize_resource_set_size(pdev, resno, size);\n \n-\tif (!bus-\u003eself)\n-\t\tgoto out;\n+\tif (bridge) {\n+\t\tret = pbus_reassign_bridge_resources(bus, res, \u0026saved);\n+\t\tif (ret)\n+\t\t\tgoto restore;\n+\t} else {\n+\t\t/* No bridge window to adjust; let the core reassign the bus. */\n+\t\tpci_bus_assign_resources(bus);\n \n-\tdown_read(\u0026pci_bus_sem);\n-\tret = pbus_reassign_bridge_resources(bus, res, \u0026saved);\n-\tif (ret)\n-\t\tgoto restore;\n+\t\tlist_for_each_entry(dev_res, \u0026saved, list) {\n+\t\t\tif (!resource_assigned(dev_res-\u003eres)) {\n+\t\t\t\tret = -ENOSPC;\n+\t\t\t\tgoto restore;\n+\t\t\t}\n+\t\t}\n+\t}\n \n out:\n \tup_read(\u0026pci_bus_sem);\n"
}

core

null

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch modifies pci_do_resource_release_and_resize() in drivers/pci/setup-bus.c, which handles PCIe Resizable BAR (REBAR) reconfiguration. This function is only invoked during probe of physical discrete GPUs (amdgpu, i915, xe) or via the sysfs resource\u003cN\u003e_resize attribute. The sysfs attribute and the underlying helper are only accessible for devices advertising the PCIe Resizable BAR extended capability (PCI_EXT_CAP_ID_REBAR or PCI_EXT_CAP_ID_VF_REBAR), which requires physical PCIe hardware (e.g., discrete GPUs) and is not implemented or emulated by any virtual device in standard virtualized fuzzing environments (QEMU / GCE). Consequently, the modified code is structurally unreachable for syzkaller.",
  "WorthFuzzing": false
}

You are an expert Linux kernel maintainer and security engineer.
Your job is to review a provided patch series and evaluate whether it warrants fuzzing with syzkaller.

IMPORTANT: The changes have ALREADY been applied and committed as the HEAD commit in
your workspace. Do NOT rely on internal assumptions. You must actively use your code access
tools to inspect the actual source code, callers, and surrounding context.

================================================================================
1. CORE TRIAGE PHILOSOPHY
================================================================================
The goal of patch fuzzing is to discover crashes, regressions, exposed latent bugs,
and newly triggered assertions introduced by the patch series.

- REACHABILITY IS THE PRIMARY GATE:
  Fuzzing can only discover bugs in code that can actually execute in standard virtualized
  environments (GCE or QEMU, utilizing software-emulated devices like USB gadgets, netdev, tun/tap).
  If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed,
  regardless of whether it adds assertions or complex logic.

- DO NOT BLINDLY TRUST "NO FUNCTIONAL CHANGE" (NFCI) OR "REFACTORING" CLAIMS:
  Patch authors routinely label changes as "cleanups", "refactorings", or state
  "No functional change intended". Do NOT take these claims at face value.
  Code refactorings that rearrange logic, introduce helper functions, or alter state management
  in core subsystems frequently introduce subtle semantic shifts or uncover latent kernel bugs.
  If reachable executable code is modified or refactored, it MUST be fuzzed.

- NEW OR MODIFIED ASSERTIONS IN REACHABLE CODE MUST BE FUZZED:
  When a patch introduces or modifies runtime checks or assertions (e.g., WARN_ON*, VM_WARN_ON*,
  BUG_ON*, lockdep_assert*) in reachable code paths, it enforces new or stricter invariants.
  Even if the author believes the invariant always holds, fuzzing is essential to verify whether
  an unusual sequence of operations can violate it.

================================================================================
2. WHEN TO RETURN WorthFuzzing=false (NEGATIVE CRITERIA)
================================================================================
Return WorthFuzzing=false ONLY IF all modified code falls strictly into one or more of these categories:

- Non-kernel and non-executable changes:
  * Modifications to Documentation/, comments, or spelling fixes.
  * User-space directories, self-tests, samples, or scripts (e.g., tools/, samples/, scripts/, usr/)
    that do not affect the compiled kernel image (vmlinux) or kernel modules.
  * Purely decorative logging (e.g., message strings in pr_err, printk, dev_info) or tracepoints
    that do not alter control flow or data structures.
  * Build system or Kconfig changes that do not alter compiled C logic.
- Structurally unreachable hardware:
  * Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed,
    ionic, amdgpu) requiring physical ASIC/PCIe cards not emulated in standard QEMU.
- Unreachable execution paths:
  * Driver teardown callbacks (.remove, .shutdown, pci_unregister_driver) executed only during
    physical PCI hot-unplug or manual sysfs driver unbinding.
  * Code paths exclusive to architectures other than the target architecture.

================================================================================
3. WHEN TO RETURN WorthFuzzing=true (POSITIVE CRITERIA)
================================================================================
Return WorthFuzzing=true whenever the patch touches reachable executable code, including:
- Core Subsystems:
  * Any logic modifications in memory management (mm/), synchronization/locking (kernel/locking/),
    BPF, scheduler, core networking, VFS, or syscall handling.
- Refactorings and Code Cleanups:
  * Any restructuring of reachable data structures, helper abstractions, or algorithm flows.
- Runtime Assertions and Defensive Checks:
  * Any introduction or alteration of assertions (WARN_ON*, VM_WARN_ON*, BUG_ON*, etc.) in reachable paths.
- Reachable Drivers and Protocols:
  * Drivers accessible via virtual buses (virtio, USB gadget, loopback, netlink, binder, sockets, etc.).

================================================================================
4. EXTRACTING FocusSymbols (PREVENTING DILUTION)
================================================================================
When WorthFuzzing=true, you must extract specific kernel functions into FocusSymbols to guide the fuzzer:

- AVOID UBIQUITOUS LIFECYCLE HOT-PATHS:
  Do NOT list generic, ubiquitous functions called by almost every program in the corpus
  (including, but not limited to: general memory allocators and deallocators, page fault
  and trap handlers, or core synchronization primitives; this is not an exhaustive list).
  Listing ubiquitous functions causes the fuzzer to classify thousands of unrelated tests as "focused",
  which severely dilutes fuzzing effort away from the actual changes.

- TARGET SPECIFIC FEATURE LOGIC AND ENTRYPOINTS:
  List functions that specifically implement the logic being added or altered, or direct API entrypoints
  for the subsystem feature under review.

- HANDLING STATIC INLINE FUNCTIONS IN HEADERS (.h):
  Compiler-inlined static functions (such as static inlines in mm/*.h or include/linux/*.h) lack
  distinct symbol addresses in vmlinux and cannot be targeted directly by symbol coverage filters.
  If the changes are primarily in static inline helpers, identify non-static, feature-specific caller
  functions in .c files that exercise them (avoiding ubiquitous lifecycle wrappers).

================================================================================
5. IDENTIFYING EnableConfigs
================================================================================
Identify any specific CONFIG_ options required to properly compile and reach the modified code:
- Inspect Kconfig files and #ifdef guards; do not make assumptions.
- Check "depends on" lines in Kconfig to include any non-standard parent subsystem configs needed.
- Strip any 'CONFIG_' prefix (e.g., return "NET_IPV4" instead of "CONFIG_NET_IPV4").
Prefer calling several tools at the same time to save round-trips.


Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.

Target architecture: amd64

For your convenience, here is the diff of the changes:
commit c8c5fa29195aaa5aab551f0f9a459dd7c4fb8a00
Author: syz-cluster <triage@syzkaller.com>
Date:   Wed Sep 16 01:50:50 2026 +0000

    syz-cluster: applied patch under review

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index e8c94aa1d3c12..ed16ef7c26fa7 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -2380,6 +2380,7 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size
 	struct resource *res = pci_resource_n(pdev, resno);
 	struct pci_dev_resource *dev_res;
 	struct pci_bus *bus = pdev->bus;
+	struct pci_dev *bridge = pci_upstream_bridge(pdev);
 	struct resource *b_win, *r;
 	LIST_HEAD(saved);
 	unsigned int i;
@@ -2397,6 +2398,8 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size
 	if (ret)
 		return ret;
 
+	down_read(&pci_bus_sem);
+
 	pci_dev_for_each_resource(pdev, r, i) {
 		if (i >= PCI_BRIDGE_RESOURCES)
 			break;
@@ -2415,13 +2418,21 @@ int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size
 
 	pci_resize_resource_set_size(pdev, resno, size);
 
-	if (!bus->self)
-		goto out;
+	if (bridge) {
+		ret = pbus_reassign_bridge_resources(bus, res, &saved);
+		if (ret)
+			goto restore;
+	} else {
+		/* No bridge window to adjust; let the core reassign the bus. */
+		pci_bus_assign_resources(bus);
 
-	down_read(&pci_bus_sem);
-	ret = pbus_reassign_bridge_resources(bus, res, &saved);
-	if (ret)
-		goto restore;
+		list_for_each_entry(dev_res, &saved, list) {
+			if (!resource_assigned(dev_res->res)) {
+				ret = -ENOSPC;
+				goto restore;
+			}
+		}
+	}
 
 out:
 	up_read(&pci_bus_sem);

gemini-3.8-flash

null

null

							input: 3319
							output: 39
							thoughts: 89
						

**Analyzing the PCI Resource Release Patch**

Okay, let's dive in. First, I need to understand exactly what this patch is doing. The diff points me towards `drivers/pci/setup-bus.c` and specifically the `pci_do_resource_release_and_resize` function. I recognize that function name; it's related to how we handle resource allocation and deallocation for PCI devices, a critical area.

To get a handle on the changes and the surrounding code, I'll need to see the context. I'll reach for either `read-file` or `grepper` – probably starting with `read-file` to get a quick overview. I need to zero in on line 2380 and the area around it in `drivers/pci/setup-bus.c`. That should give me the relevant code and the surrounding logic to understand the purpose and implications of these modifications. Hopefully, this should clarify the potential impact on resource management within the PCI subsystem.

{
  "File": "drivers/pci/setup-bus.c",
  "FirstLine": 2370,
  "LineCount": 90
}

{
  "Contents": "2370:\t\n2371:\t\t\tpci_setup_bridge(dev-\u003esubordinate);\n2372:\t\t}\n2373:\t\n2374:\t\treturn 0;\n2375:\t}\n2376:\t\n2377:\tint pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size,\n2378:\t\t\t\t\t       int exclude_bars)\n2379:\t{\n2380:\t\tstruct resource *res = pci_resource_n(pdev, resno);\n2381:\t\tstruct pci_dev_resource *dev_res;\n2382:\t\tstruct pci_bus *bus = pdev-\u003ebus;\n2383:\t\tstruct pci_dev *bridge = pci_upstream_bridge(pdev);\n2384:\t\tstruct resource *b_win, *r;\n2385:\t\tLIST_HEAD(saved);\n2386:\t\tunsigned int i;\n2387:\t\tint old, ret;\n2388:\t\n2389:\t\tb_win = pbus_select_window(bus, res);\n2390:\t\tif (!b_win)\n2391:\t\t\treturn -EINVAL;\n2392:\t\n2393:\t\told = pci_rebar_get_current_size(pdev, resno);\n2394:\t\tif (old \u003c 0)\n2395:\t\t\treturn old;\n2396:\t\n2397:\t\tret = pci_rebar_set_size(pdev, resno, size);\n2398:\t\tif (ret)\n2399:\t\t\treturn ret;\n2400:\t\n2401:\t\tdown_read(\u0026pci_bus_sem);\n2402:\t\n2403:\t\tpci_dev_for_each_resource(pdev, r, i) {\n2404:\t\t\tif (i \u003e= PCI_BRIDGE_RESOURCES)\n2405:\t\t\t\tbreak;\n2406:\t\n2407:\t\t\tif (exclude_bars \u0026 BIT(i))\n2408:\t\t\t\tcontinue;\n2409:\t\n2410:\t\t\tif (b_win != pbus_select_window(bus, r))\n2411:\t\t\t\tcontinue;\n2412:\t\n2413:\t\t\tret = pci_dev_res_add_to_list(\u0026saved, pdev, r, 0, 0);\n2414:\t\t\tif (ret)\n2415:\t\t\t\tgoto restore;\n2416:\t\t\tpci_release_resource(pdev, i);\n2417:\t\t}\n2418:\t\n2419:\t\tpci_resize_resource_set_size(pdev, resno, size);\n2420:\t\n2421:\t\tif (bridge) {\n2422:\t\t\tret = pbus_reassign_bridge_resources(bus, res, \u0026saved);\n2423:\t\t\tif (ret)\n2424:\t\t\t\tgoto restore;\n2425:\t\t} else {\n2426:\t\t\t/* No bridge window to adjust; let the core reassign the bus. */\n2427:\t\t\tpci_bus_assign_resources(bus);\n2428:\t\n2429:\t\t\tlist_for_each_entry(dev_res, \u0026saved, list) {\n2430:\t\t\t\tif (!resource_assigned(dev_res-\u003eres)) {\n2431:\t\t\t\t\tret = -ENOSPC;\n2432:\t\t\t\t\tgoto restore;\n2433:\t\t\t\t}\n2434:\t\t\t}\n2435:\t\t}\n2436:\t\n2437:\tout:\n2438:\t\tup_read(\u0026pci_bus_sem);\n2439:\t\tpci_dev_res_free_list(\u0026saved);\n2440:\t\treturn ret;\n2441:\t\n2442:\trestore:\n2443:\t\t/*\n2444:\t\t * Revert to the old configuration.\n2445:\t\t *\n2446:\t\t * BAR Size must be restored first because it affects the read-only\n2447:\t\t * bits in BAR (the old address might not be restorable otherwise\n2448:\t\t * due to low address bits).\n2449:\t\t */\n2450:\t\tpci_rebar_set_size(pdev, resno, old);\n2451:\t\n2452:\t\tlist_for_each_entry(dev_res, \u0026saved, list) {\n2453:\t\t\tstruct resource *res = dev_res-\u003eres;\n2454:\t\t\tstruct pci_dev *dev = dev_res-\u003edev;\n2455:\t\n2456:\t\t\ti = pci_resource_num(dev, res);\n2457:\t\n2458:\t\t\tif (resource_assigned(res)) {\n2459:\t\t\t\trelease_child_resources(res);\n"
}

gemini-3.8-flash

null

null

							input: 4942
							output: 26
							thoughts: 31
						

Here's my attempt at summarizing the thought process, as if I were having it:

**Digging into Resource Management**

Okay, so I'm looking at `pci_do_resource_release_and_resize`. Sounds like a critical function for PCI resource management – which means it's likely involved in a lot of core driver interactions. Now, the real question is, how widely is it used? I need to understand the call graph to get a sense of its impact and potential consequences of any changes. Time to whip out the trusty grep. Let's find out exactly *where* this function is being invoked. I'll need to know the contexts to understand this properly.

{
  "Expression": "pci_do_resource_release_and_resize"
}

{
  "Output": "drivers/pci/pci.h=508=void pci_resize_resource_set_size(struct pci_dev *dev, int resno, int size);\ndrivers/pci/pci.h:509:int pci_do_resource_release_and_resize(struct pci_dev *dev, int resno, int size,\ndrivers/pci/pci.h-510-\t\t\t\t       int exclude_bars);\n--\ndrivers/pci/rebar.c=298=int pci_resize_resource(struct pci_dev *dev, int resno, int size,\n--\ndrivers/pci/rebar.c-313-\ndrivers/pci/rebar.c:314:\treturn pci_do_resource_release_and_resize(dev, resno, size, exclude_bars);\ndrivers/pci/rebar.c-315-}\n--\ndrivers/pci/setup-bus.c=2308=static int pbus_reassign_bridge_resources(struct pci_bus *bus, struct resource *res,\n--\ndrivers/pci/setup-bus.c-2376-\ndrivers/pci/setup-bus.c:2377:int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size,\ndrivers/pci/setup-bus.c-2378-\t\t\t\t       int exclude_bars)\n"
}

gemini-3.8-flash

null

null

							input: 5511
							output: 20
							thoughts: 16
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Investigating `pci_resize_resource` Usage**

Alright, let's dive in. I need to understand the implications of this function, `pci_resize_resource`. My first instinct is to immediately trace its call sites. Where is this thing being *used*? That's the crucial context. Understanding the callers gives me a handle on the intended purpose and, critically, any potential side effects of modifying or even just observing `pci_resize_resource`. It's all about following the flow of execution and identifying those points of interaction. That's where the real complexity, and any potential issues, will lie. So, let's get those call graphs compiled.

{
  "Expression": "pci_resize_resource"
}

{
  "Output": "drivers/gpu/drm/amd/amdgpu/amdgpu_device.c=1091=int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)\n--\ndrivers/gpu/drm/amd/amdgpu/amdgpu_device.c-1156-\ndrivers/gpu/drm/amd/amdgpu/amdgpu_device.c:1157:\tr = pci_resize_resource(adev-\u003epdev, 0, rbar_size,\ndrivers/gpu/drm/amd/amdgpu/amdgpu_device.c-1158-\t\t\t\t(adev-\u003easic_type \u003e= CHIP_BONAIRE) ? 1 \u003c\u003c 5\n--\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c=24=_resize_bar(struct drm_i915_private *i915, int resno, resource_size_t size)\n--\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c-29-\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c:30:\tret = pci_resize_resource(pdev, resno, bar_size, 0);\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c-31-\tif (ret) {\n--\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c=40=static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t lmem_size)\n--\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c-85-\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c:86:\t/* pci_resize_resource will fail anyways */\ndrivers/gpu/drm/i915/gt/intel_region_lmem.c-87-\tif (!root_res) {\n--\ndrivers/gpu/drm/xe/xe_pci_rebar.c=15=static void resize_bar(struct xe_device *xe, int resno, resource_size_t size)\n--\ndrivers/gpu/drm/xe/xe_pci_rebar.c-20-\ndrivers/gpu/drm/xe/xe_pci_rebar.c:21:\tret = pci_resize_resource(pdev, resno, bar_size, 0);\ndrivers/gpu/drm/xe/xe_pci_rebar.c-22-\tif (ret) {\n--\ndrivers/pci/iov.c=1329=EXPORT_SYMBOL_GPL(pci_sriov_configure_simple);\n--\ndrivers/pci/iov.c-1337- * Set the new size of a VF BAR that supports VF resizable BAR capability.\ndrivers/pci/iov.c:1338: * Unlike pci_resize_resource(), this does not cause the resource that\ndrivers/pci/iov.c-1339- * reserves the MMIO space (originally up to total_VFs) to be resized, which\n--\ndrivers/pci/pci-sysfs.c=1727=static ssize_t __resource_resize_store(struct device *dev, int n,\n--\ndrivers/pci/pci-sysfs.c-1762-\ndrivers/pci/pci-sysfs.c:1763:\tret = pci_resize_resource(pdev, n, size, 0);\ndrivers/pci/pci-sysfs.c-1764-\tif (ret)\n--\ndrivers/pci/pci.h=506=void pci_put_host_bridge_device(struct device *dev);\ndrivers/pci/pci.h-507-\ndrivers/pci/pci.h:508:void pci_resize_resource_set_size(struct pci_dev *dev, int resno, int size);\ndrivers/pci/pci.h-509-int pci_do_resource_release_and_resize(struct pci_dev *dev, int resno, int size,\n--\ndrivers/pci/rebar.c=254=static bool pci_resize_is_memory_decoding_enabled(struct pci_dev *dev,\n--\ndrivers/pci/rebar.c-266-\ndrivers/pci/rebar.c:267:void pci_resize_resource_set_size(struct pci_dev *dev, int resno, int size)\ndrivers/pci/rebar.c-268-{\n--\ndrivers/pci/rebar.c-278-/**\ndrivers/pci/rebar.c:279: * pci_resize_resource - reconfigure a Resizable BAR and resources\ndrivers/pci/rebar.c-280- * @dev: the PCI device\n--\ndrivers/pci/rebar.c-297- */\ndrivers/pci/rebar.c:298:int pci_resize_resource(struct pci_dev *dev, int resno, int size,\ndrivers/pci/rebar.c-299-\t\t\tint exclude_bars)\n--\ndrivers/pci/rebar.c-315-}\ndrivers/pci/rebar.c:316:EXPORT_SYMBOL(pci_resize_resource);\n--\ndrivers/pci/setup-bus.c=2377=int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size,\n--\ndrivers/pci/setup-bus.c-2418-\ndrivers/pci/setup-bus.c:2419:\tpci_resize_resource_set_size(pdev, resno, size);\ndrivers/pci/setup-bus.c-2420-\n--\ninclude/linux/pci.h=1502=int pci_rebar_get_max_size(struct pci_dev *pdev, int bar);\ninclude/linux/pci.h:1503:int __must_check pci_resize_resource(struct pci_dev *dev, int i, int size,\ninclude/linux/pci.h-1504-\t\t\t\t     int exclude_bars);\n"
}

gemini-3.8-flash

null

null

							input: 7297
							output: 41
							thoughts: 48
						

Here's my analysis of the provided snippet, as if it were my thought process:

**Diving into the PCI Subsystem's Sysfs Interface**

Okay, so we're looking at some code related to the PCI subsystem's sysfs interface. Specifically, the file and line number given, `drivers/pci/pci-sysfs.c:1763`, points to a crucial area. Hmm, given that context, it might be helpful to zoom out slightly. Let me focus on the surrounding code, perhaps around line 1727 of `drivers/pci/pci-sysfs.c`. I need to understand the function this line is within and understand the flow of logic around it to gain full context. I'm going to quickly check what's upstream and downstream in terms of function calls and variable assignments. The sysfs interface for PCI devices is a complex beast, and understanding the surrounding structure is vital before I zero in on that specific line.

{
  "File": "drivers/pci/pci-sysfs.c",
  "FirstLine": 1725,
  "LineCount": 60
}

{
  "Contents": "1725:\t}\n1726:\t\n1727:\tstatic ssize_t __resource_resize_store(struct device *dev, int n,\n1728:\t\t\t\t\t       const char *buf, size_t count)\n1729:\t{\n1730:\t\tstruct pci_dev *pdev = to_pci_dev(dev);\n1731:\t\tstruct pci_bus *bus = pdev-\u003ebus;\n1732:\t\tunsigned long size;\n1733:\t\tint ret;\n1734:\t\tu16 cmd;\n1735:\t\n1736:\t\tif (!capable(CAP_SYS_ADMIN))\n1737:\t\t\treturn -EPERM;\n1738:\t\n1739:\t\tif (kstrtoul(buf, 0, \u0026size) \u003c 0)\n1740:\t\t\treturn -EINVAL;\n1741:\t\n1742:\t\tdevice_lock(dev);\n1743:\t\tif (dev-\u003edriver || pci_num_vf(pdev)) {\n1744:\t\t\tret = -EBUSY;\n1745:\t\t\tgoto unlock;\n1746:\t\t}\n1747:\t\n1748:\t\tpci_config_pm_runtime_get(pdev);\n1749:\t\n1750:\t\tif ((pdev-\u003eclass \u003e\u003e 8) == PCI_CLASS_DISPLAY_VGA) {\n1751:\t\t\tret = aperture_remove_conflicting_pci_devices(pdev,\n1752:\t\t\t\t\t\t\t\"resourceN_resize\");\n1753:\t\t\tif (ret)\n1754:\t\t\t\tgoto pm_put;\n1755:\t\t}\n1756:\t\n1757:\t\tpci_read_config_word(pdev, PCI_COMMAND, \u0026cmd);\n1758:\t\tpci_write_config_word(pdev, PCI_COMMAND,\n1759:\t\t\t\t      cmd \u0026 ~PCI_COMMAND_MEMORY);\n1760:\t\n1761:\t\tsysfs_remove_groups(\u0026pdev-\u003edev.kobj, pci_dev_resource_attr_groups);\n1762:\t\n1763:\t\tret = pci_resize_resource(pdev, n, size, 0);\n1764:\t\tif (ret)\n1765:\t\t\tpci_warn(pdev, \"Failed to resize BAR %d: %pe\\n\",\n1766:\t\t\t\t n, ERR_PTR(ret));\n1767:\t\n1768:\t\tpci_assign_unassigned_bus_resources(bus);\n1769:\t\n1770:\t\tif (sysfs_create_groups(\u0026pdev-\u003edev.kobj, pci_dev_resource_attr_groups))\n1771:\t\t\tpci_warn(pdev, \"Failed to recreate resource groups after BAR resizing\\n\");\n1772:\t\n1773:\t\tpci_write_config_word(pdev, PCI_COMMAND, cmd);\n1774:\tpm_put:\n1775:\t\tpci_config_pm_runtime_put(pdev);\n1776:\tunlock:\n1777:\t\tdevice_unlock(dev);\n1778:\t\n1779:\t\treturn ret ? ret : count;\n1780:\t}\n1781:\t\n1782:\t#define pci_dev_resource_resize_attr(n)\t\t\t\t\t\\\n1783:\tstatic ssize_t resource##n##_resize_show(struct device *dev,\t\t\\\n1784:\t\t\t\t\t\t struct device_attribute *attr,\t\\\n"
}

gemini-3.8-flash

null

null

							input: 8528
							output: 28
							thoughts: 42
						

Okay, let's break this down.

**Investigating Resizable BARs in PCI Devices**

Alright, so the `resourceN_resize` sysfs attribute... that's the key indicator for resizable Base Address Registers (BARs) on PCI devices, assuming the device supports the feature. My first thought is: when is this attribute actually *created*? Need to dig deeper and figure out the exact moment the system exposes this interface. Understanding the creation point will be crucial for any practical application or debugging I might undertake related to resizable BARs. Time to trace the code and see what triggers it.

{
  "Expression": "resource.*_resize",
  "PathPrefix": "drivers/pci"
}

{
  "Output": "drivers/pci/pci-sysfs.c=1706=static const struct attribute_group pci_dev_reset_method_attr_group = {\n--\ndrivers/pci/pci-sysfs.c-1711-#if defined(HAVE_PCI_MMAP) || defined(ARCH_GENERIC_PCI_MMAP_RESOURCE)\ndrivers/pci/pci-sysfs.c:1712:static ssize_t __resource_resize_show(struct device *dev, int n, char *buf)\ndrivers/pci/pci-sysfs.c-1713-{\n--\ndrivers/pci/pci-sysfs.c-1726-\ndrivers/pci/pci-sysfs.c:1727:static ssize_t __resource_resize_store(struct device *dev, int n,\ndrivers/pci/pci-sysfs.c-1728-\t\t\t\t       const char *buf, size_t count)\n--\ndrivers/pci/pci-sysfs.c-1751-\t\tret = aperture_remove_conflicting_pci_devices(pdev,\ndrivers/pci/pci-sysfs.c:1752:\t\t\t\t\t\t\"resourceN_resize\");\ndrivers/pci/pci-sysfs.c-1753-\t\tif (ret)\n--\ndrivers/pci/pci-sysfs.c-1781-\ndrivers/pci/pci-sysfs.c:1782:#define pci_dev_resource_resize_attr(n)\t\t\t\t\t\\\ndrivers/pci/pci-sysfs.c:1783:static ssize_t resource##n##_resize_show(struct device *dev,\t\t\\\ndrivers/pci/pci-sysfs.c-1784-\t\t\t\t\t struct device_attribute *attr,\t\\\n--\ndrivers/pci/pci-sysfs.c-1786-{\t\t\t\t\t\t\t\t\t\\\ndrivers/pci/pci-sysfs.c:1787:\treturn __resource_resize_show(dev, n, buf);\t\t\t\\\ndrivers/pci/pci-sysfs.c-1788-}\t\t\t\t\t\t\t\t\t\\\ndrivers/pci/pci-sysfs.c:1789:static ssize_t resource##n##_resize_store(struct device *dev,\t\t\\\ndrivers/pci/pci-sysfs.c-1790-\t\t\t\t\t  struct device_attribute *attr,\\\n--\ndrivers/pci/pci-sysfs.c-1792-{\t\t\t\t\t\t\t\t\t\\\ndrivers/pci/pci-sysfs.c:1793:\treturn __resource_resize_store(dev, n, buf, count);\t\t\\\ndrivers/pci/pci-sysfs.c-1794-}\t\t\t\t\t\t\t\t\t\\\ndrivers/pci/pci-sysfs.c:1795:static DEVICE_ATTR_RW(resource##n##_resize)\ndrivers/pci/pci-sysfs.c-1796-\ndrivers/pci/pci-sysfs.c:1797:pci_dev_resource_resize_attr(0);\ndrivers/pci/pci-sysfs.c:1798:pci_dev_resource_resize_attr(1);\ndrivers/pci/pci-sysfs.c:1799:pci_dev_resource_resize_attr(2);\ndrivers/pci/pci-sysfs.c:1800:pci_dev_resource_resize_attr(3);\ndrivers/pci/pci-sysfs.c:1801:pci_dev_resource_resize_attr(4);\ndrivers/pci/pci-sysfs.c:1802:pci_dev_resource_resize_attr(5);\ndrivers/pci/pci-sysfs.c-1803-\ndrivers/pci/pci-sysfs.c:1804:static struct attribute *resource_resize_attrs[] = {\ndrivers/pci/pci-sysfs.c:1805:\t\u0026dev_attr_resource0_resize.attr,\ndrivers/pci/pci-sysfs.c:1806:\t\u0026dev_attr_resource1_resize.attr,\ndrivers/pci/pci-sysfs.c:1807:\t\u0026dev_attr_resource2_resize.attr,\ndrivers/pci/pci-sysfs.c:1808:\t\u0026dev_attr_resource3_resize.attr,\ndrivers/pci/pci-sysfs.c:1809:\t\u0026dev_attr_resource4_resize.attr,\ndrivers/pci/pci-sysfs.c:1810:\t\u0026dev_attr_resource5_resize.attr,\ndrivers/pci/pci-sysfs.c-1811-\tNULL,\n--\ndrivers/pci/pci-sysfs.c-1813-\ndrivers/pci/pci-sysfs.c:1814:static umode_t resource_resize_attr_is_visible(struct kobject *kobj,\ndrivers/pci/pci-sysfs.c-1815-\t\t\t\t\t  struct attribute *a, int n)\n--\ndrivers/pci/pci-sysfs.c-1821-\ndrivers/pci/pci-sysfs.c:1822:static const struct attribute_group pci_dev_resource_resize_attr_group = {\ndrivers/pci/pci-sysfs.c:1823:\t.attrs = resource_resize_attrs,\ndrivers/pci/pci-sysfs.c:1824:\t.is_visible = resource_resize_attr_is_visible,\ndrivers/pci/pci-sysfs.c-1825-};\n--\ndrivers/pci/pci-sysfs.c=1895=const struct attribute_group *pci_dev_groups[] = {\n--\ndrivers/pci/pci-sysfs.c-1900-\t\u0026pci_dev_resource_wc_attr_group,\ndrivers/pci/pci-sysfs.c:1901:\t\u0026pci_dev_resource_resize_attr_group,\ndrivers/pci/pci-sysfs.c-1902-#endif\n--\ndrivers/pci/pci.h=508=void pci_resize_resource_set_size(struct pci_dev *dev, int resno, int size);\ndrivers/pci/pci.h:509:int pci_do_resource_release_and_resize(struct pci_dev *dev, int resno, int size,\ndrivers/pci/pci.h-510-\t\t\t\t       int exclude_bars);\n--\ndrivers/pci/rebar.c=298=int pci_resize_resource(struct pci_dev *dev, int resno, int size,\n--\ndrivers/pci/rebar.c-313-\ndrivers/pci/rebar.c:314:\treturn pci_do_resource_release_and_resize(dev, resno, size, exclude_bars);\ndrivers/pci/rebar.c-315-}\n--\ndrivers/pci/setup-bus.c=2308=static int pbus_reassign_bridge_resources(struct pci_bus *bus, struct resource *res,\n--\ndrivers/pci/setup-bus.c-2376-\ndrivers/pci/setup-bus.c:2377:int pci_do_resource_release_and_resize(struct pci_dev *pdev, int resno, int size,\ndrivers/pci/setup-bus.c-2378-\t\t\t\t       int exclude_bars)\n"
}

gemini-3.8-flash

null

null

							input: 10643
							output: 41
							thoughts: 37
						

Here's my take:

**Analyzing the Resource Resizing Visibility**

Okay, so I'm looking at this `resource_resize_attr_is_visible` function. Right, it's pretty clear where to go to find it: `drivers/pci/pci-sysfs.c`. I need to understand the logic behind when and why this attribute is visible, presumably through sysfs. It's time to dive into that file and see what conditions need to be met. I'm expecting to find some checks related to capabilities, device state, perhaps access permissions or if the system even supports resizing in the first place. I need to figure out the exact criteria this function uses to determine whether or not a user can see this specific resource attribute. Let's get cracking.

{
  "File": "drivers/pci/pci-sysfs.c",
  "FirstLine": 1812,
  "LineCount": 20
}

{
  "Contents": "1812:\t};\n1813:\t\n1814:\tstatic umode_t resource_resize_attr_is_visible(struct kobject *kobj,\n1815:\t\t\t\t\t\t  struct attribute *a, int n)\n1816:\t{\n1817:\t\tstruct pci_dev *pdev = to_pci_dev(kobj_to_dev(kobj));\n1818:\t\n1819:\t\treturn pci_rebar_get_current_size(pdev, n) \u003c 0 ? 0 : a-\u003emode;\n1820:\t}\n1821:\t\n1822:\tstatic const struct attribute_group pci_dev_resource_resize_attr_group = {\n1823:\t\t.attrs = resource_resize_attrs,\n1824:\t\t.is_visible = resource_resize_attr_is_visible,\n1825:\t};\n1826:\t#endif\n1827:\t\n1828:\tstatic struct attribute *pci_dev_dev_attrs[] = {\n1829:\t\t\u0026dev_attr_boot_vga.attr,\n1830:\t\t\u0026dev_attr_serial_number.attr,\n1831:\t\tNULL,\n"
}

gemini-3.8-flash

null

null

							input: 11216
							output: 35
							thoughts: 61
						

**Analyzing Rebar Size Retrieval**

Okay, so I'm digging into this `pci_rebar_get_current_size(pdev, n)` function. The core question is, when does this thing return a value greater than or equal to zero? That's what I need to understand for this particular scenario. Time to dive into the source code, specifically `drivers/pci/rebar.c`. Let's see what that function is doing internally and what conditions determine its return value. This should illuminate the logic behind the size retrieval. I'm hoping to quickly identify the potential edge cases or error conditions to fully grasp the behavior.

{
  "File": "drivers/pci/rebar.c",
  "FirstLine": 1,
  "LineCount": 80
}

{
  "Contents": "   1:\t// SPDX-License-Identifier: GPL-2.0\n   2:\t/*\n   3:\t * PCI Resizable BAR Extended Capability handling.\n   4:\t */\n   5:\t\n   6:\t#include \u003clinux/bits.h\u003e\n   7:\t#include \u003clinux/bitfield.h\u003e\n   8:\t#include \u003clinux/bitops.h\u003e\n   9:\t#include \u003clinux/errno.h\u003e\n  10:\t#include \u003clinux/export.h\u003e\n  11:\t#include \u003clinux/ioport.h\u003e\n  12:\t#include \u003clinux/log2.h\u003e\n  13:\t#include \u003clinux/pci.h\u003e\n  14:\t#include \u003clinux/sizes.h\u003e\n  15:\t#include \u003clinux/types.h\u003e\n  16:\t\n  17:\t#include \"pci.h\"\n  18:\t\n  19:\t#define PCI_REBAR_MIN_SIZE\t((resource_size_t)SZ_1M)\n  20:\t\n  21:\t/**\n  22:\t * pci_rebar_bytes_to_size - Convert size in bytes to PCI BAR Size\n  23:\t * @bytes: size in bytes\n  24:\t *\n  25:\t * Convert size in bytes to encoded BAR Size in Resizable BAR Capability\n  26:\t * (PCIe r6.2, sec. 7.8.6.3).\n  27:\t *\n  28:\t * Return: encoded BAR Size as defined in the PCIe spec (0=1MB, 31=128TB)\n  29:\t */\n  30:\tint pci_rebar_bytes_to_size(u64 bytes)\n  31:\t{\n  32:\t\tint rebar_minsize = ilog2(PCI_REBAR_MIN_SIZE);\n  33:\t\n  34:\t\tbytes = roundup_pow_of_two(bytes);\n  35:\t\n  36:\t\treturn max(ilog2(bytes), rebar_minsize) - rebar_minsize;\n  37:\t}\n  38:\tEXPORT_SYMBOL_GPL(pci_rebar_bytes_to_size);\n  39:\t\n  40:\t/**\n  41:\t * pci_rebar_size_to_bytes - Convert encoded BAR Size to size in bytes\n  42:\t * @size: encoded BAR Size as defined in the PCIe spec (0=1MB, 31=128TB)\n  43:\t *\n  44:\t * Return: BAR size in bytes\n  45:\t */\n  46:\tresource_size_t pci_rebar_size_to_bytes(int size)\n  47:\t{\n  48:\t\treturn 1ULL \u003c\u003c (size + ilog2(PCI_REBAR_MIN_SIZE));\n  49:\t}\n  50:\tEXPORT_SYMBOL_GPL(pci_rebar_size_to_bytes);\n  51:\t\n  52:\tvoid pci_rebar_init(struct pci_dev *pdev)\n  53:\t{\n  54:\t\tpdev-\u003erebar_cap = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);\n  55:\t}\n  56:\t\n  57:\t/**\n  58:\t * pci_rebar_find_pos - find position of resize control reg for BAR\n  59:\t * @pdev: PCI device\n  60:\t * @bar: BAR to find\n  61:\t *\n  62:\t * Helper to find the position of the control register for a BAR.\n  63:\t *\n  64:\t * Return:\n  65:\t * * %-ENOTSUPP if resizable BARs are not supported at all,\n  66:\t * * %-ENOENT if no control register for the BAR could be found.\n  67:\t */\n  68:\tstatic int pci_rebar_find_pos(struct pci_dev *pdev, int bar)\n  69:\t{\n  70:\t\tunsigned int pos, nbars, i;\n  71:\t\tu32 ctrl;\n  72:\t\n  73:\t\tif (pci_resource_is_iov(bar)) {\n  74:\t\t\tpos = pci_iov_vf_rebar_cap(pdev);\n  75:\t\t\tbar = pci_resource_num_to_vf_bar(bar);\n  76:\t\t} else {\n  77:\t\t\tpos = pdev-\u003erebar_cap;\n  78:\t\t}\n  79:\t\n  80:\t\tif (!pos)\n"
}

gemini-3.8-flash

null

null

							input: 12632
							output: 24
							thoughts: 1933
						

**Analyzing Resizable BAR (ReBAR) Support and Vulnerabilities**

Okay, let's break this down. First, I'm checking for the presence of the PCIe Resizable BAR capability (`PCI_EXT_CAP_ID_REBAR`) on a PCI device using `pci_find_ext_capability`. This is the starting point. Can we trigger ReBAR on devices in QEMU/syzkaller? That's the key question. We need to identify devices and their drivers. I'm focusing on `pci_do_resource_release_and_resize`, as that seems like a likely entry point for any ReBAR manipulation.

Now, my initial thought is: Let's see if we can find relevant context in the commit history for `pci_do_resource_release_and_resize` itself. My immediate goal is to look at changes to understand what the code is *doing*. I'm digging into the tools available (or rather, *not* available). Since I can't use `git log`, I need to utilize what's there, so I'll utilize the available search tools to examine the patch itself.

Analyzing the diff, I'm noticing a significant change: the code's logic is shifting based on whether a bridge exists (`pci_upstream_bridge`). Before, it seems like if the device was directly on the root bus (`!bus->self`), a resource resize would *effectively* be a no-op, just setting the size and returning. It skipped the resource reassignment entirely. The change introduces a `bridge` check. If a bridge exists, it calls `pbus_reassign_bridge_resources`; otherwise, it calls `pci_bus_assign_resources`. The critical observation here is that `down_read(&pci_bus_sem)` is moved *up* in the call path. This implies a change in the locking behavior, which could be interesting.

The original code's behavior: If a device was directly on the root bus (`bus->self == NULL`), the resource was not reassigned. It simply set the BAR size. It seems ReBAR configuration was skipped if on the root bus.

The patch implements a new resource assignment method. Instead of `bus->self`, it checks for an upstream bridge device. If no bridge, then the `pci_bus_assign_resources` method is now called.

Next, I need to know which callers trigger `pci_resize_resource` or `pci_do_resource_release_and_resize`. I'm starting a call site analysis. I'm seeing AMDGPU, Intel i915, and Intel Xe drivers are involved (`amdgpu_device_resize_fb_bar`, `i915_resize_lmem_bar`, `resize_bar`). That implies, in these cases, it relates to actual physical hardware. `amdgpu` definitely requires physical hardware. And `i915` is mostly focused on discrete GPUs.

However, I find something interesting: `drivers/pci/pci-sysfs.c`. This connects to sysfs entries, namely `resource%d_resize`. Now, I'm asking: Is this `resource%d_resize` available on any device in syzkaller/QEMU, the virtual test environment? It's time to enumerate the PCI devices available in the standard QEMU configurations (q35 or i440fx). I start listing the usual suspects: Virtio devices, network adapters, storage controllers, USB controllers, graphics adapters, etc. My focus is to determine if *any* of those devices have ReBAR support. Now, I need to check where `PCI_EXT_CAP_ID_REBAR` is defined in QEMU or kernel, to see if anything in my device list supports it.

{
  "Expression": "PCI_EXT_CAP_ID_REBAR"
}

{
  "Output": "drivers/pci/controller/dwc/pcie-designware-ep.c=372=static unsigned int dw_pcie_ep_get_rebar_offset(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-378-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:379:\toffset = dw_pcie_ep_find_ext_capability(ep, func_no, PCI_EXT_CAP_ID_REBAR);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-380-\tif (!offset)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1200=static void dw_pcie_ep_init_rebar_registers(struct dw_pcie_ep *ep, u8 func_no)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1209-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1210:\toffset = dw_pcie_ep_find_ext_capability(ep, func_no, PCI_EXT_CAP_ID_REBAR);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1211-\n--\ndrivers/pci/rebar.c=52=void pci_rebar_init(struct pci_dev *pdev)\ndrivers/pci/rebar.c-53-{\ndrivers/pci/rebar.c:54:\tpdev-\u003erebar_cap = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_REBAR);\ndrivers/pci/rebar.c-55-}\n--\ndrivers/vfio/pci/vfio_pci_config.c=71=static const u16 pci_ext_cap_length[PCI_EXT_CAP_ID_MAX + 1] = {\n--\ndrivers/vfio/pci/vfio_pci_config.c-91-\t[PCI_EXT_CAP_ID_AMD_XXX] =\t0,\t/* not yet */\ndrivers/vfio/pci/vfio_pci_config.c:92:\t[PCI_EXT_CAP_ID_REBAR]\t=\t0xFF,\ndrivers/vfio/pci/vfio_pci_config.c-93-\t[PCI_EXT_CAP_ID_DPA]\t=\t0xFF,\n--\ndrivers/vfio/pci/vfio_pci_config.c=1399=static int vfio_ext_cap_len(struct vfio_pci_core_device *vdev, u16 ecap, u16 epos)\n--\ndrivers/vfio/pci/vfio_pci_config.c-1436-\ndrivers/vfio/pci/vfio_pci_config.c:1437:\tcase PCI_EXT_CAP_ID_REBAR:\ndrivers/vfio/pci/vfio_pci_config.c-1438-\t\tret = pci_read_config_byte(pdev, epos + PCI_REBAR_CTRL, \u0026byte);\n--\ninclude/uapi/linux/pci_regs.h-745-#define PCI_EXT_CAP_ID_AMD_XXX\t0x14\t/* Reserved for AMD */\ninclude/uapi/linux/pci_regs.h:746:#define PCI_EXT_CAP_ID_REBAR\t0x15\t/* Resizable BAR */\ninclude/uapi/linux/pci_regs.h-747-#define PCI_EXT_CAP_ID_DPA\t0x16\t/* Dynamic Power Allocation */\n"
}

gemini-3.8-flash

null

null

							input: 16359
							output: 19
							thoughts: 127
						

**My QEMU and syzkaller REBAR Musings**

Okay, hold on a second. When I think about PCIe emulation, the first thing that jumps to mind is QEMU. But does QEMU, in all its flexibility, actually emulate *any* PCIe device with Resizable BAR (REBAR) support? I can't immediately recall seeing that feature specifically called out. I need to clarify that crucial detail: does QEMU even *support* the REBAR capability, even in theory?

Let me re-frame the question: QEMU has robust PCIe device emulation, we know that. But are there *any* emulated devices within QEMU that actually implement the REBAR functionality? My instinct is no. Even if QEMU *did* theoretically have REBAR, which of its emulated devices *would* implement it? I can't picture any. Maybe something related to Compute Express Link (CXL), if anything? Or maybe absolutely nothing has that capability right now.

Wait a moment, what about syzkaller? It's a kernel fuzzer, and I *know* it's involved in PCI fuzzing. Could it potentially emulate PCI devices, even if it's not its primary function? I need to explore that.

Okay, let's step back, does syzkaller *actually* have PCI emulation capabilities, even in a limited way? I need to check my references quickly. The next step is clear: I'll fire up `syz-grepper` and search for mentions of "pci" or "rebar". That should give me the answer quickly.

tool "syz-grepper" does not exist, please correct the name

{
  "Expression": "pci"
}

{
  "error": "tool \"syz-grepper\" does not exist, please correct the name"
}

gemini-3.8-flash

null

null

							input: 16880
							output: 25
							thoughts: 331
						

**My Thought Process on Tool Availability and PCI BARs**

Okay, first things first. The instructions explicitly said *not* to use `syz-grepper` to search specific syzkaller descriptions. I noted that, and the instruction said to use it in other cases. Looking at the tool declarations, I can see that `syz-grepper` isn't *actually* listed. I've only got `grepper`, `codesearch-dir-index`, `read-file`, and `set-results` declared. So, it looks like it's not available, even though the instructions say it *can* be used. That's good to keep in mind for later tasks, especially if syzkaller descriptions become important.

Now, shifting gears, I need to check for the presence of mock/virtual PCI drivers or tests, focusing on resizable BARs. I remember we were looking at this before. I already grepped for `PCI_EXT_CAP_ID_REBAR` earlier. I see the results are:
- `drivers/pci/controller/dwc/pcie-designware-ep.c`
- `drivers/pci/rebar.c`
- `drivers/vfio/pci/vfio_pci_config.c`
- `include/uapi/linux/pci_regs.h`

Alright, that's a good starting point. Now I need to see about SR-IOV VF resizable BARs, so let's look for `pci_iov_vf_rebar_cap` too.

{
  "Expression": "pci_iov_vf_rebar_cap"
}

{
  "Output": "drivers/pci/iov.c=931=static void sriov_restore_vf_rebar_state(struct pci_dev *dev)\n--\ndrivers/pci/iov.c-935-\ndrivers/pci/iov.c:936:\tpos = pci_iov_vf_rebar_cap(dev);\ndrivers/pci/iov.c-937-\tif (!pos)\n--\ndrivers/pci/pci.h=996=bool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev);\ndrivers/pci/pci.h:997:static inline u16 pci_iov_vf_rebar_cap(struct pci_dev *dev)\ndrivers/pci/pci.h-998-{\n--\ndrivers/pci/pci.h=1038=static inline bool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev)\n--\ndrivers/pci/pci.h-1041-}\ndrivers/pci/pci.h:1042:static inline u16 pci_iov_vf_rebar_cap(struct pci_dev *dev)\ndrivers/pci/pci.h-1043-{\n--\ndrivers/pci/rebar.c=68=static int pci_rebar_find_pos(struct pci_dev *pdev, int bar)\n--\ndrivers/pci/rebar.c-73-\tif (pci_resource_is_iov(bar)) {\ndrivers/pci/rebar.c:74:\t\tpos = pci_iov_vf_rebar_cap(pdev);\ndrivers/pci/rebar.c-75-\t\tbar = pci_resource_num_to_vf_bar(bar);\n"
}

gemini-3.8-flash

null

null

							input: 18041
							output: 37
							thoughts: 29
						

Here's my take on the thought process, as if it were my own:

**Investigating the PCI IOV Virtual Function Rebar Capability**

Okay, time to dig into this. I'm going to start by confirming the definition of `pci_iov_vf_rebar_cap`. Let's jump into the `drivers/pci/pci.h` header file. It's the logical place to start looking for this if it involves PCI and IOV, specifically Virtual Functions, and ReBAR, which strongly suggests that the capability in question is probably a capability extension. Let's see what the definition reveals about its structure, meaning, and any associated constants or structures. This header should provide the fundamental building blocks I need to understand this functionality better. From there I can move into the relevant drivers and see how it is used and handled.

{
  "File": "drivers/pci/pci.h",
  "FirstLine": 995,
  "LineCount": 20
}

{
  "Contents": " 995:\tvoid pci_iov_resource_set_size(struct pci_dev *dev, int resno, int size);\n 996:\tbool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev);\n 997:\tstatic inline u16 pci_iov_vf_rebar_cap(struct pci_dev *dev)\n 998:\t{\n 999:\t\tif (!dev-\u003eis_physfn)\n1000:\t\t\treturn 0;\n1001:\t\n1002:\t\treturn dev-\u003esriov-\u003evf_rebar_cap;\n1003:\t}\n1004:\tstatic inline bool pci_resource_is_iov(int resno)\n1005:\t{\n1006:\t\treturn resno \u003e= PCI_IOV_RESOURCES \u0026\u0026 resno \u003c= PCI_IOV_RESOURCE_END;\n1007:\t}\n1008:\tstatic inline int pci_resource_num_from_vf_bar(int resno)\n1009:\t{\n1010:\t\treturn resno + PCI_IOV_RESOURCES;\n1011:\t}\n1012:\tstatic inline int pci_resource_num_to_vf_bar(int resno)\n1013:\t{\n1014:\t\treturn resno - PCI_IOV_RESOURCES;\n"
}

gemini-3.8-flash

null

null

							input: 18654
							output: 20
							thoughts: 18
						

Here's my attempt at summarizing the thought process, tailored for an expert audience:

**Debugging `vf_rebar_cap` Initialization**

Okay, hold on a second. I need to backtrack here. I'm looking at this code and I'm seeing `vf_rebar_cap` used, but I'm not immediately grasping where the initial value is set. I'm going to quickly trace this. Let's see...where does the variable `vf_rebar_cap` get initialized? I need to understand the data flow here to reason about the implications of how it's being used further downstream. Gotta dig into this and find the originating assignment.

{
  "Expression": "vf_rebar_cap"
}

{
  "Output": "drivers/pci/iov.c=796=static int sriov_init(struct pci_dev *dev, int pos)\n--\ndrivers/pci/iov.c-891-\t\tiov-\u003elink = PCI_DEVFN(PCI_SLOT(dev-\u003edevfn), iov-\u003elink);\ndrivers/pci/iov.c:892:\tiov-\u003evf_rebar_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_VF_REBAR);\ndrivers/pci/iov.c-893-\n--\ndrivers/pci/iov.c=931=static void sriov_restore_vf_rebar_state(struct pci_dev *dev)\n--\ndrivers/pci/iov.c-935-\ndrivers/pci/iov.c:936:\tpos = pci_iov_vf_rebar_cap(dev);\ndrivers/pci/iov.c-937-\tif (!pos)\n--\ndrivers/pci/pci.h=697=struct pci_sriov {\n--\ndrivers/pci/pci.h-718-\tresource_size_t\tbarsz[PCI_SRIOV_NUM_BARS];\t/* VF BAR size */\ndrivers/pci/pci.h:719:\tu16\t\tvf_rebar_cap;\t/* VF Resizable BAR capability offset */\ndrivers/pci/pci.h-720-\tbool\t\tdrivers_autoprobe; /* Auto probing of VFs by driver */\n--\ndrivers/pci/pci.h=996=bool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev);\ndrivers/pci/pci.h:997:static inline u16 pci_iov_vf_rebar_cap(struct pci_dev *dev)\ndrivers/pci/pci.h-998-{\n--\ndrivers/pci/pci.h-1001-\ndrivers/pci/pci.h:1002:\treturn dev-\u003esriov-\u003evf_rebar_cap;\ndrivers/pci/pci.h-1003-}\n--\ndrivers/pci/pci.h=1038=static inline bool pci_iov_is_memory_decoding_enabled(struct pci_dev *dev)\n--\ndrivers/pci/pci.h-1041-}\ndrivers/pci/pci.h:1042:static inline u16 pci_iov_vf_rebar_cap(struct pci_dev *dev)\ndrivers/pci/pci.h-1043-{\n--\ndrivers/pci/rebar.c=68=static int pci_rebar_find_pos(struct pci_dev *pdev, int bar)\n--\ndrivers/pci/rebar.c-73-\tif (pci_resource_is_iov(bar)) {\ndrivers/pci/rebar.c:74:\t\tpos = pci_iov_vf_rebar_cap(pdev);\ndrivers/pci/rebar.c-75-\t\tbar = pci_resource_num_to_vf_bar(bar);\n"
}

gemini-3.8-flash

null

null

							input: 19636
							output: 37
							thoughts: 43
						

Here's my analysis of the provided text, rendered in the first person, assuming an expert user:

**Deep Dive into `drivers/pci/rebar.c`**

Okay, hold on a second. I need to get a handle on this. Let me pull up `drivers/pci/rebar.c`. Right, let's just go through the whole file. I need to understand the ReBAR implementation in the kernel. I'll read every line, meticulously examining the logic flow, the data structures used, and, critically, the call sites. Where is this functionality invoked? What are the entry points? Are there any subtle interactions with other PCI subsystems that I need to be aware of? I'll be looking for potential conflicts, performance bottlenecks, and any areas that might require tuning or further investigation. This will be a methodical examination. Time to roll up my sleeves and dig in.

{
  "File": "drivers/pci/rebar.c",
  "FirstLine": 80,
  "LineCount": 100
}

{
  "Contents": "  80:\t\tif (!pos)\n  81:\t\t\treturn -ENOTSUPP;\n  82:\t\n  83:\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, \u0026ctrl);\n  84:\t\tnbars = FIELD_GET(PCI_REBAR_CTRL_NBAR_MASK, ctrl);\n  85:\t\n  86:\t\tfor (i = 0; i \u003c nbars; i++, pos += 8) {\n  87:\t\t\tint bar_idx;\n  88:\t\n  89:\t\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, \u0026ctrl);\n  90:\t\t\tbar_idx = FIELD_GET(PCI_REBAR_CTRL_BAR_IDX, ctrl);\n  91:\t\t\tif (bar_idx == bar)\n  92:\t\t\t\treturn pos;\n  93:\t\t}\n  94:\t\n  95:\t\treturn -ENOENT;\n  96:\t}\n  97:\t\n  98:\t/**\n  99:\t * pci_rebar_get_possible_sizes - get possible sizes for Resizable BAR\n 100:\t * @pdev: PCI device\n 101:\t * @bar: BAR to query\n 102:\t *\n 103:\t * Get the possible sizes of a resizable BAR as bitmask.\n 104:\t *\n 105:\t * Return: A bitmask of possible sizes (bit 0=1MB, bit 31=128TB), or %0 if\n 106:\t *\t   BAR isn't resizable.\n 107:\t */\n 108:\tu64 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar)\n 109:\t{\n 110:\t\tint pos;\n 111:\t\tu32 cap;\n 112:\t\n 113:\t\tpos = pci_rebar_find_pos(pdev, bar);\n 114:\t\tif (pos \u003c 0)\n 115:\t\t\treturn 0;\n 116:\t\n 117:\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CAP, \u0026cap);\n 118:\t\tcap = FIELD_GET(PCI_REBAR_CAP_SIZES, cap);\n 119:\t\n 120:\t\t/* Sapphire RX 5600 XT Pulse has an invalid cap dword for BAR 0 */\n 121:\t\tif (pdev-\u003evendor == PCI_VENDOR_ID_ATI \u0026\u0026 pdev-\u003edevice == 0x731f \u0026\u0026\n 122:\t\t    bar == 0 \u0026\u0026 cap == 0x700)\n 123:\t\t\treturn 0x3f00;\n 124:\t\n 125:\t\treturn cap;\n 126:\t}\n 127:\tEXPORT_SYMBOL(pci_rebar_get_possible_sizes);\n 128:\t\n 129:\t/**\n 130:\t * pci_rebar_size_supported - check if size is supported for BAR\n 131:\t * @pdev: PCI device\n 132:\t * @bar: BAR to check\n 133:\t * @size: encoded size as defined in the PCIe spec (0=1MB, 31=128TB)\n 134:\t *\n 135:\t * Return: %true if @bar is resizable and @size is supported, otherwise\n 136:\t *\t   %false.\n 137:\t */\n 138:\tbool pci_rebar_size_supported(struct pci_dev *pdev, int bar, int size)\n 139:\t{\n 140:\t\tu64 sizes = pci_rebar_get_possible_sizes(pdev, bar);\n 141:\t\n 142:\t\tif (size \u003c 0 || size \u003e ilog2(SZ_128T) - ilog2(PCI_REBAR_MIN_SIZE))\n 143:\t\t\treturn false;\n 144:\t\n 145:\t\treturn BIT(size) \u0026 sizes;\n 146:\t}\n 147:\tEXPORT_SYMBOL_GPL(pci_rebar_size_supported);\n 148:\t\n 149:\t/**\n 150:\t * pci_rebar_get_max_size - get the maximum supported size of a BAR\n 151:\t * @pdev: PCI device\n 152:\t * @bar: BAR to query\n 153:\t *\n 154:\t * Get the largest supported size of a resizable BAR as a size.\n 155:\t *\n 156:\t * Return: the encoded maximum BAR size as defined in the PCIe spec\n 157:\t *\t   (0=1MB, 31=128TB), or %-NOENT on error.\n 158:\t */\n 159:\tint pci_rebar_get_max_size(struct pci_dev *pdev, int bar)\n 160:\t{\n 161:\t\tu64 sizes;\n 162:\t\n 163:\t\tsizes = pci_rebar_get_possible_sizes(pdev, bar);\n 164:\t\tif (!sizes)\n 165:\t\t\treturn -ENOENT;\n 166:\t\n 167:\t\treturn __fls(sizes);\n 168:\t}\n 169:\tEXPORT_SYMBOL_GPL(pci_rebar_get_max_size);\n 170:\t\n 171:\t/**\n 172:\t * pci_rebar_get_current_size - get the current size of a Resizable BAR\n 173:\t * @pdev: PCI device\n 174:\t * @bar: BAR to get the size from\n 175:\t *\n 176:\t * Read the current size of a BAR from the Resizable BAR config.\n 177:\t *\n 178:\t * Return: BAR Size if @bar is resizable (0=1MB, 31=128TB), or negative on\n 179:\t *         error.\n"
}

gemini-3.8-flash

null

null

							input: 21503
							output: 38
							thoughts: 18
						

Okay, here's my interpretation of that thought process, assuming I'm deep in the weeds of `drivers/pci/rebar.c`:

**Diving Back into the REBAR Code**

Alright, time to get back into `drivers/pci/rebar.c`. I've been in this area before, but a quick refresh is always good. I need to understand this section thoroughly, so let's carefully review the code. Knowing this code is going to be important to get the next task accomplished. Let's see what fresh challenges or new nuances await. Time to dig in!

{
  "File": "drivers/pci/rebar.c",
  "FirstLine": 180,
  "LineCount": 100
}

{
  "Contents": " 180:\t */\n 181:\tint pci_rebar_get_current_size(struct pci_dev *pdev, int bar)\n 182:\t{\n 183:\t\tint pos;\n 184:\t\tu32 ctrl;\n 185:\t\n 186:\t\tpos = pci_rebar_find_pos(pdev, bar);\n 187:\t\tif (pos \u003c 0)\n 188:\t\t\treturn pos;\n 189:\t\n 190:\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, \u0026ctrl);\n 191:\t\treturn FIELD_GET(PCI_REBAR_CTRL_BAR_SIZE, ctrl);\n 192:\t}\n 193:\t\n 194:\t/**\n 195:\t * pci_rebar_set_size - set a new size for a Resizable BAR\n 196:\t * @pdev: PCI device\n 197:\t * @bar: BAR to set size to\n 198:\t * @size: new size as defined in the PCIe spec (0=1MB, 31=128TB)\n 199:\t *\n 200:\t * Set the new size of a BAR as defined in the spec.\n 201:\t *\n 202:\t * Return: %0 if resizing was successful, or negative on error.\n 203:\t */\n 204:\tint pci_rebar_set_size(struct pci_dev *pdev, int bar, int size)\n 205:\t{\n 206:\t\tint pos;\n 207:\t\tu32 ctrl;\n 208:\t\n 209:\t\tpos = pci_rebar_find_pos(pdev, bar);\n 210:\t\tif (pos \u003c 0)\n 211:\t\t\treturn pos;\n 212:\t\n 213:\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, \u0026ctrl);\n 214:\t\tFIELD_MODIFY(PCI_REBAR_CTRL_BAR_SIZE, \u0026ctrl, size);\n 215:\t\tpci_write_config_dword(pdev, pos + PCI_REBAR_CTRL, ctrl);\n 216:\t\n 217:\t\tif (pci_resource_is_iov(bar))\n 218:\t\t\tpci_iov_resource_set_size(pdev, bar, size);\n 219:\t\n 220:\t\treturn 0;\n 221:\t}\n 222:\t\n 223:\tvoid pci_restore_rebar_state(struct pci_dev *pdev)\n 224:\t{\n 225:\t\tunsigned int pos, nbars, i;\n 226:\t\tu32 ctrl;\n 227:\t\n 228:\t\tpos = pdev-\u003erebar_cap;\n 229:\t\tif (!pos)\n 230:\t\t\treturn;\n 231:\t\n 232:\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, \u0026ctrl);\n 233:\t\tif (PCI_POSSIBLE_ERROR(ctrl))\n 234:\t\t\treturn;\n 235:\t\n 236:\t\tnbars = FIELD_GET(PCI_REBAR_CTRL_NBAR_MASK, ctrl);\n 237:\t\n 238:\t\tfor (i = 0; i \u003c nbars; i++, pos += 8) {\n 239:\t\t\tstruct resource *res;\n 240:\t\t\tint bar_idx, size;\n 241:\t\n 242:\t\t\tpci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, \u0026ctrl);\n 243:\t\t\tif (PCI_POSSIBLE_ERROR(ctrl))\n 244:\t\t\t\treturn;\n 245:\t\n 246:\t\t\tbar_idx = ctrl \u0026 PCI_REBAR_CTRL_BAR_IDX;\n 247:\t\t\tres = pci_resource_n(pdev, bar_idx);\n 248:\t\t\tsize = pci_rebar_bytes_to_size(resource_size(res));\n 249:\t\t\tFIELD_MODIFY(PCI_REBAR_CTRL_BAR_SIZE, \u0026ctrl, size);\n 250:\t\t\tpci_write_config_dword(pdev, pos + PCI_REBAR_CTRL, ctrl);\n 251:\t\t}\n 252:\t}\n 253:\t\n 254:\tstatic bool pci_resize_is_memory_decoding_enabled(struct pci_dev *dev,\n 255:\t\t\t\t\t\t\t  int resno)\n 256:\t{\n 257:\t\tu16 cmd;\n 258:\t\n 259:\t\tif (pci_resource_is_iov(resno))\n 260:\t\t\treturn pci_iov_is_memory_decoding_enabled(dev);\n 261:\t\n 262:\t\tpci_read_config_word(dev, PCI_COMMAND, \u0026cmd);\n 263:\t\n 264:\t\treturn cmd \u0026 PCI_COMMAND_MEMORY;\n 265:\t}\n 266:\t\n 267:\tvoid pci_resize_resource_set_size(struct pci_dev *dev, int resno, int size)\n 268:\t{\n 269:\t\tresource_size_t res_size = pci_rebar_size_to_bytes(size);\n 270:\t\tstruct resource *res = pci_resource_n(dev, resno);\n 271:\t\n 272:\t\tif (pci_resource_is_iov(resno))\n 273:\t\t\tres_size *= pci_sriov_get_totalvfs(dev);\n 274:\t\n 275:\t\tresource_set_size(res, res_size);\n 276:\t}\n 277:\t\n 278:\t/**\n 279:\t * pci_resize_resource - reconfigure a Resizable BAR and resources\n"
}

gemini-3.8-flash

null

null

							input: 23268
							output: 37
							thoughts: 28
						

Okay, here's my interpretation of what I'd be thinking as I review those lines of `drivers/pci/rebar.c`:

**Deep Dive into ReBAR Initialization**

Alright, lines 280 to 320 in `drivers/pci/rebar.c`... let's see what we're dealing with here. My intuition is that this section is likely handling the core initialization or probing phase for Resizable BAR (ReBAR) support. Given the context, I expect to find the initial detection of ReBAR capabilities, perhaps some checks to see if the system hardware supports it, and definitely the groundwork to get things rolling. I'm looking for the essential function calls and the data structures they're operating on. We're probably checking the PCI configuration space. Is this where we're querying the device's BAR registers to identify supported sizes, and if the BIOS has already done something interesting, we'll learn what's set up so far. Okay, I'm going in!

{
  "File": "drivers/pci/rebar.c",
  "FirstLine": 280,
  "LineCount": 45
}

{
  "Contents": " 280:\t * @dev: the PCI device\n 281:\t * @resno: index of the BAR to be resized\n 282:\t * @size: new size as defined in the spec (0=1MB, 31=128TB)\n 283:\t * @exclude_bars: a mask of BARs that should not be released\n 284:\t *\n 285:\t * Reconfigure @resno to @size and re-run resource assignment algorithm\n 286:\t * with the new size.\n 287:\t *\n 288:\t * Prior to resize, release @dev resources that share a bridge window with\n 289:\t * @resno.  This unpins the bridge window resource to allow changing it.\n 290:\t *\n 291:\t * The caller may prevent releasing a particular BAR by providing\n 292:\t * @exclude_bars mask, but this may result in the resize operation failing\n 293:\t * due to insufficient space.\n 294:\t *\n 295:\t * Return: 0 on success, or negative on error. In case of an error, the\n 296:\t *         resources are restored to their original places.\n 297:\t */\n 298:\tint pci_resize_resource(struct pci_dev *dev, int resno, int size,\n 299:\t\t\t\tint exclude_bars)\n 300:\t{\n 301:\t\tstruct pci_host_bridge *host;\n 302:\t\n 303:\t\t/* Check if we must preserve the firmware's resource assignment */\n 304:\t\thost = pci_find_host_bridge(dev-\u003ebus);\n 305:\t\tif (host-\u003epreserve_config)\n 306:\t\t\treturn -ENOTSUPP;\n 307:\t\n 308:\t\tif (pci_resize_is_memory_decoding_enabled(dev, resno))\n 309:\t\t\treturn -EBUSY;\n 310:\t\n 311:\t\tif (!pci_rebar_size_supported(dev, resno, size))\n 312:\t\t\treturn -EINVAL;\n 313:\t\n 314:\t\treturn pci_do_resource_release_and_resize(dev, resno, size, exclude_bars);\n 315:\t}\n 316:\tEXPORT_SYMBOL(pci_resize_resource);\n"
}

gemini-3.8-flash

null

null

							input: 24177
							output: 26
							thoughts: 2951
						

**Analysis of `pci_resize_resource` Reachability in Standard Virtualized Environments**

Okay, here's the breakdown of my thought process. I need to determine if the changes in `drivers/pci/setup-bus.c` are relevant for fuzzing, given that reachability is the primary gate. I'm focusing on whether `pci_do_resource_release_and_resize` (and consequently, `pci_resize_resource`) can be triggered in standard environments like QEMU or GCE.

First, I identified the call sites of `pci_resize_resource`. I see it's triggered during `amdgpu`, `i915`, and `xe` probes, all related to GPU drivers. Then, there's the sysfs entry `/sys/bus/pci/devices/.../resourceN_resize`. My initial question is whether that sysfs entry can even exist in a VM without a physical GPU.

I dug deeper into the sysfs case. The visibility of the sysfs entry hinges on `pci_rebar_get_current_size()`, which ultimately calls `pci_rebar_find_pos()`. This function relies on `pdev->rebar_cap`, which is set by `pci_find_ext_capability()` searching for `PCI_EXT_CAP_ID_REBAR`. This is a PCI Extended Capability, and I know those are only on PCIe devices.

So, the key question becomes: does QEMU (or standard GCE setups) emulate a PCIe device with the REBAR capability? I examined the QEMU source code. Does QEMU implement REBAR? I need to check which QEMU PCIe devices have `PCI_EXT_CAP_ID_REBAR`. I also considered CXL, but that's a different technology. I need to remember the syzkaller environment, which uses `-machine pc` or `-machine q35`. I know syzkaller adds specific virtual devices like `e1000` and `virtio-rng-pci`, but do any of those have REBAR? I need to know if any emulated PCI device in QEMU supports resizable BARs.

I then revisited the patch. I see the main change relates to how resources are reassigned when a device with resizable BARs is directly connected to the root complex (e.g., a GPU plugged directly into the CPU). In such cases, if a bridge isn't present (`!bus->self`), resources were previously *not* reassigned, leading to broken BAR resizing. The patch fixes this by calling `pci_bus_assign_resources()`. This suggests it is a device on the root bus with no upstream bridge.

Next, I looked at the fuzzing guidelines. My goal is to determine if the modified code is *reachable*. I have to check if the code falls under the "structurally unreachable hardware" category.

I reviewed every caller of `pci_resize_resource`. The GPU drivers (amdgpu, i915, xe) are highly unlikely to be emulated in standard QEMU or GCE. The remaining case is the sysfs entry. I traced the visibility condition for the sysfs entry. It relies on `pci_rebar_get_current_size()`, which checks for the REBAR capability. Does any QEMU device expose that?

I searched the kernel for other instances of `PCI_EXT_CAP_ID_REBAR` and `PCI_EXT_CAP_ID_VF_REBAR`. I found a few: Synopsys DesignWare PCIe Endpoint controller, the core rebar implementation, and VFIO. VFIO is interesting as it does emulate PCI config spaces. I concluded that, based on my understanding, that there are no standard QEMU devices. I need to know if any software-emulated device or virtual device has `PCI_EXT_CAP_ID_REBAR`.

The goal is to determine if a call to the patch can be reached in the standard fuzzing environment. Given that REBAR is a GPU feature and my knowledge of QEMU, I concluded that, under standard QEMU, it is likely *unreachable* without some custom QEMU configuration. So, by the fuzzing guidelines, the code is structurally unreachable and not worth fuzzing.

{
  "Expression": "PCI_EXT_CAP_ID_VF_REBAR"
}

{
  "Output": "drivers/pci/iov.c=796=static int sriov_init(struct pci_dev *dev, int pos)\n--\ndrivers/pci/iov.c-891-\t\tiov-\u003elink = PCI_DEVFN(PCI_SLOT(dev-\u003edevfn), iov-\u003elink);\ndrivers/pci/iov.c:892:\tiov-\u003evf_rebar_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_VF_REBAR);\ndrivers/pci/iov.c-893-\n--\ninclude/uapi/linux/pci_regs.h-756-#define PCI_EXT_CAP_ID_DVSEC\t0x23\t/* Designated Vendor-Specific */\ninclude/uapi/linux/pci_regs.h:757:#define PCI_EXT_CAP_ID_VF_REBAR 0x24\t/* VF Resizable BAR */\ninclude/uapi/linux/pci_regs.h-758-#define PCI_EXT_CAP_ID_DLF\t0x25\t/* Data Link Feature */\n"
}

gemini-3.8-flash

null

null

							input: 28356
							output: 20
							thoughts: 3515
						

**Analysis of Fuzzing Reachability for PCI Resource Resizing**

Okay, so I need to figure out if this patch to `drivers/pci/setup-bus.c` is fuzzable by syzkaller.  My initial thought is that it touches only `drivers/pci/iov.c` and `include/uapi/linux/pci_regs.h`. My immediate concern is, does QEMU or GCE provide any device that actually *has* the PCIe Resizable BAR capability (`PCI_EXT_CAP_ID_REBAR`)?  I know from experience that standard QEMU doesn't emulate anything like that. I've checked the standard QEMU devices: virtio-* (PCIe or legacy PCI), e1000e, igb, nvme (QEMU's NVMe doesn't use REBAR, NVMe spec has fixed BAR sizes), and xhci – none of them have it. It is clear that QEMU doesn't have REBAR in ANY virtual device. GCE's virtual hardware (gVNIC, virtio-scsi / nvme, etc.) also doesn't provide REBAR unless a physical GPU is attached via PCIe passthrough (which is not what syzkaller runs). I also know that there are negative criteria (Section 2) for what should *not* be fuzzed.

Now I need to carefully consider Section 2's negative criteria, and Section 3's positive criteria. Specifically, the wording in Section 1 is crucial: "If the modified code is structurally unreachable (see Section 2), it MUST NOT be fuzzed, regardless of whether it adds assertions or complex logic." The negative criteria mention "Structurally unreachable hardware: Vendor-specific PCIe switches, SmartNICs, or GPU drivers... requiring physical ASIC/PCIe cards not emulated in standard QEMU." This is the key.

Let's check `drivers/pci/setup-bus.c`'s role in normal boot or bus assignment, and, specifically, the modified function, `pci_do_resource_release_and_resize`. Looking at the diff, that function is modified. But, is it called during a normal bus scan or during boot? I have to analyze where `pci_do_resource_release_and_resize` is *actually* used.

I did a deep search, and it turns out that `pci_do_resource_release_and_resize` is *only* called by `pci_resize_resource` which is in `drivers/pci/rebar.c` and can be called by 1) `amdgpu_device_resize_fb_bar`, 2) `_resize_bar` (i915), 3) `resize_bar` (xe), and 4) `__resource_resize_store`. I need to now figure out if syzkaller can reach those!

Specifically, can it reach `__resource_resize_store`?  Can syzkaller invoke `pci_do_resource_release_and_resize` without a device that actually reports the PCIe Resizable BAR capability?  I need to check how `__resource_resize_store` is invoked. It looks like it only runs if the `resourceN_resize` sysfs file exists, and that file only exists if the device supports `PCI_EXT_CAP_ID_REBAR` or `PCI_EXT_CAP_ID_VF_REBAR`. Even *if* I were to call this function directly (which I cannot), the code checks `pci_rebar_size_supported`, which internally checks for `pci_rebar_find_pos`. That function returns a value indicating if REBAR is present. If `pdev->rebar_cap` is zero, or if it isn't set, then the check fails and returns `-EINVAL`.  This means `pci_do_resource_release_and_resize` is *never* reached. This means that if there is not a device with `PCI_EXT_CAP_ID_REBAR`, the core function `pci_do_resource_release_and_resize` is unreachable!

I need to confirm if `pci_do_resource_release_and_resize` itself is exported, which it isn't.  The function is an internal driver function declared in `drivers/pci/pci.h`. Only `drivers/pci/rebar.c` calls it and even if it was callable it would require `pci_rebar_get_current_size(pdev, resno) >= 0` and `pci_rebar_set_size(pdev, resno, size) ==

{
  "Expression": "pci_epc_"
}

{
  "Output": "\nFull output is too long, showing 500 out of 2608 lines.\nUse more precise expression if possible.\n\nDocumentation/PCI/endpoint/pci-endpoint.rst=42=by the PCI controller driver.\nDocumentation/PCI/endpoint/pci-endpoint.rst-43-\nDocumentation/PCI/endpoint/pci-endpoint.rst:44:* devm_pci_epc_create()/pci_epc_create()\nDocumentation/PCI/endpoint/pci-endpoint.rst-45-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-57-   The PCI controller driver can then create a new EPC device by invoking\nDocumentation/PCI/endpoint/pci-endpoint.rst:58:   devm_pci_epc_create()/pci_epc_create().\nDocumentation/PCI/endpoint/pci-endpoint.rst-59-\nDocumentation/PCI/endpoint/pci-endpoint.rst:60:* pci_epc_destroy()\nDocumentation/PCI/endpoint/pci-endpoint.rst-61-\nDocumentation/PCI/endpoint/pci-endpoint.rst-62-   The PCI controller driver can destroy the EPC device created by\nDocumentation/PCI/endpoint/pci-endpoint.rst:63:   pci_epc_create() using pci_epc_destroy().\nDocumentation/PCI/endpoint/pci-endpoint.rst-64-\nDocumentation/PCI/endpoint/pci-endpoint.rst:65:* pci_epc_linkup()\nDocumentation/PCI/endpoint/pci-endpoint.rst-66-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-68-   they are linked has established a link with the host, the PCI controller\nDocumentation/PCI/endpoint/pci-endpoint.rst:69:   driver should invoke pci_epc_linkup().\nDocumentation/PCI/endpoint/pci-endpoint.rst-70-\nDocumentation/PCI/endpoint/pci-endpoint.rst:71:* pci_epc_mem_init()\nDocumentation/PCI/endpoint/pci-endpoint.rst-72-\nDocumentation/PCI/endpoint/pci-endpoint.rst:73:   Initialize the pci_epc_mem structure used for allocating EPC addr space.\nDocumentation/PCI/endpoint/pci-endpoint.rst-74-\nDocumentation/PCI/endpoint/pci-endpoint.rst:75:* pci_epc_mem_exit()\nDocumentation/PCI/endpoint/pci-endpoint.rst-76-\nDocumentation/PCI/endpoint/pci-endpoint.rst:77:   Cleanup the pci_epc_mem structure allocated during pci_epc_mem_init().\nDocumentation/PCI/endpoint/pci-endpoint.rst-78-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst=84=by the PCI endpoint function driver.\nDocumentation/PCI/endpoint/pci-endpoint.rst-85-\nDocumentation/PCI/endpoint/pci-endpoint.rst:86:* pci_epc_write_header()\nDocumentation/PCI/endpoint/pci-endpoint.rst-87-\nDocumentation/PCI/endpoint/pci-endpoint.rst:88:   The PCI endpoint function driver should use pci_epc_write_header() to\nDocumentation/PCI/endpoint/pci-endpoint.rst-89-   write the standard configuration header to the endpoint controller.\nDocumentation/PCI/endpoint/pci-endpoint.rst-90-\nDocumentation/PCI/endpoint/pci-endpoint.rst:91:* pci_epc_set_bar()\nDocumentation/PCI/endpoint/pci-endpoint.rst-92-\nDocumentation/PCI/endpoint/pci-endpoint.rst:93:   The PCI endpoint function driver should use pci_epc_set_bar() to configure\nDocumentation/PCI/endpoint/pci-endpoint.rst-94-   the Base Address Register in order for the host to assign PCI addr space.\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-97-\nDocumentation/PCI/endpoint/pci-endpoint.rst:98:   Some endpoint controllers also support calling pci_epc_set_bar() again\nDocumentation/PCI/endpoint/pci-endpoint.rst:99:   for the same BAR (without calling pci_epc_clear_bar()) to update inbound\nDocumentation/PCI/endpoint/pci-endpoint.rst-100-   address translations after the host has programmed the BAR base address.\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-109-   feature, it requires that the BAR base address has been programmed by\nDocumentation/PCI/endpoint/pci-endpoint.rst:110:   the host during enumeration. Thus, it needs to call pci_epc_set_bar()\nDocumentation/PCI/endpoint/pci-endpoint.rst-111-   twice for the same BAR (requires dynamic_inbound_mapping): first with\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-116-   Note that when making use of the inbound subrange mapping feature, the\nDocumentation/PCI/endpoint/pci-endpoint.rst:117:   EPF driver must not call pci_epc_clear_bar() between the two\nDocumentation/PCI/endpoint/pci-endpoint.rst:118:   pci_epc_set_bar() calls, because clearing the BAR can clear/disable the\nDocumentation/PCI/endpoint/pci-endpoint.rst-119-   BAR register or BAR decode on the endpoint while the host still expects\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-121-\nDocumentation/PCI/endpoint/pci-endpoint.rst:122:* pci_epc_clear_bar()\nDocumentation/PCI/endpoint/pci-endpoint.rst-123-\nDocumentation/PCI/endpoint/pci-endpoint.rst:124:   The PCI endpoint function driver should use pci_epc_clear_bar() to reset\nDocumentation/PCI/endpoint/pci-endpoint.rst-125-   the BAR.\nDocumentation/PCI/endpoint/pci-endpoint.rst-126-\nDocumentation/PCI/endpoint/pci-endpoint.rst:127:* pci_epc_raise_irq()\nDocumentation/PCI/endpoint/pci-endpoint.rst-128-\nDocumentation/PCI/endpoint/pci-endpoint.rst:129:   The PCI endpoint function driver should use pci_epc_raise_irq() to raise\nDocumentation/PCI/endpoint/pci-endpoint.rst-130-   Legacy Interrupt, MSI or MSI-X Interrupt.\nDocumentation/PCI/endpoint/pci-endpoint.rst-131-\nDocumentation/PCI/endpoint/pci-endpoint.rst:132:* pci_epc_mem_alloc_addr()\nDocumentation/PCI/endpoint/pci-endpoint.rst-133-\nDocumentation/PCI/endpoint/pci-endpoint.rst:134:   The PCI endpoint function driver should use pci_epc_mem_alloc_addr(), to\nDocumentation/PCI/endpoint/pci-endpoint.rst-135-   allocate memory address from EPC addr space which is required to access\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-137-\nDocumentation/PCI/endpoint/pci-endpoint.rst:138:* pci_epc_mem_free_addr()\nDocumentation/PCI/endpoint/pci-endpoint.rst-139-\nDocumentation/PCI/endpoint/pci-endpoint.rst:140:   The PCI endpoint function driver should use pci_epc_mem_free_addr() to\nDocumentation/PCI/endpoint/pci-endpoint.rst:141:   free the memory space allocated using pci_epc_mem_alloc_addr().\nDocumentation/PCI/endpoint/pci-endpoint.rst-142-\nDocumentation/PCI/endpoint/pci-endpoint.rst:143:* pci_epc_map_addr()\nDocumentation/PCI/endpoint/pci-endpoint.rst-144-\nDocumentation/PCI/endpoint/pci-endpoint.rst:145:  A PCI endpoint function driver should use pci_epc_map_addr() to map to a RC\nDocumentation/PCI/endpoint/pci-endpoint.rst-146-  PCI address the CPU address of local memory obtained with\nDocumentation/PCI/endpoint/pci-endpoint.rst:147:  pci_epc_mem_alloc_addr().\nDocumentation/PCI/endpoint/pci-endpoint.rst-148-\nDocumentation/PCI/endpoint/pci-endpoint.rst:149:* pci_epc_unmap_addr()\nDocumentation/PCI/endpoint/pci-endpoint.rst-150-\nDocumentation/PCI/endpoint/pci-endpoint.rst:151:  A PCI endpoint function driver should use pci_epc_unmap_addr() to unmap the\nDocumentation/PCI/endpoint/pci-endpoint.rst:152:  CPU address of local memory mapped to a RC address with pci_epc_map_addr().\nDocumentation/PCI/endpoint/pci-endpoint.rst-153-\nDocumentation/PCI/endpoint/pci-endpoint.rst:154:* pci_epc_mem_map()\nDocumentation/PCI/endpoint/pci-endpoint.rst-155-\nDocumentation/PCI/endpoint/pci-endpoint.rst-156-  A PCI endpoint controller may impose constraints on the RC PCI addresses that\nDocumentation/PCI/endpoint/pci-endpoint.rst:157:  can be mapped. The function pci_epc_mem_map() allows endpoint function\nDocumentation/PCI/endpoint/pci-endpoint.rst-158-  drivers to allocate and map controller memory while handling such\nDocumentation/PCI/endpoint/pci-endpoint.rst-159-  constraints. This function will determine the size of the memory that must be\nDocumentation/PCI/endpoint/pci-endpoint.rst:160:  allocated with pci_epc_mem_alloc_addr() for successfully mapping a RC PCI\nDocumentation/PCI/endpoint/pci-endpoint.rst-161-  address range. This function will also indicate the size of the PCI address\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-165-\nDocumentation/PCI/endpoint/pci-endpoint.rst:166:* pci_epc_mem_unmap()\nDocumentation/PCI/endpoint/pci-endpoint.rst-167-\nDocumentation/PCI/endpoint/pci-endpoint.rst:168:  A PCI endpoint function driver can use pci_epc_mem_unmap() to unmap and free\nDocumentation/PCI/endpoint/pci-endpoint.rst:169:  controller memory that was allocated and mapped using pci_epc_mem_map().\nDocumentation/PCI/endpoint/pci-endpoint.rst-170-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst=177=using these APIs.\nDocumentation/PCI/endpoint/pci-endpoint.rst-178-\nDocumentation/PCI/endpoint/pci-endpoint.rst:179:* pci_epc_get()\nDocumentation/PCI/endpoint/pci-endpoint.rst-180-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-183-\nDocumentation/PCI/endpoint/pci-endpoint.rst:184:* pci_epc_put()\nDocumentation/PCI/endpoint/pci-endpoint.rst-185-\nDocumentation/PCI/endpoint/pci-endpoint.rst-186-   Release the reference to the PCI endpoint controller obtained using\nDocumentation/PCI/endpoint/pci-endpoint.rst:187:   pci_epc_get()\nDocumentation/PCI/endpoint/pci-endpoint.rst-188-\nDocumentation/PCI/endpoint/pci-endpoint.rst:189:* pci_epc_add_epf()\nDocumentation/PCI/endpoint/pci-endpoint.rst-190-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-193-\nDocumentation/PCI/endpoint/pci-endpoint.rst:194:* pci_epc_remove_epf()\nDocumentation/PCI/endpoint/pci-endpoint.rst-195-\n--\nDocumentation/PCI/endpoint/pci-endpoint.rst-197-\nDocumentation/PCI/endpoint/pci-endpoint.rst:198:* pci_epc_start()\nDocumentation/PCI/endpoint/pci-endpoint.rst-199-\nDocumentation/PCI/endpoint/pci-endpoint.rst:200:   The PCI endpoint function driver should invoke pci_epc_start() once it\nDocumentation/PCI/endpoint/pci-endpoint.rst-201-   has configured the endpoint function and wants to start the PCI link.\nDocumentation/PCI/endpoint/pci-endpoint.rst-202-\nDocumentation/PCI/endpoint/pci-endpoint.rst:203:* pci_epc_stop()\nDocumentation/PCI/endpoint/pci-endpoint.rst-204-\nDocumentation/PCI/endpoint/pci-endpoint.rst:205:   The PCI endpoint function driver should invoke pci_epc_stop() to stop\nDocumentation/PCI/endpoint/pci-endpoint.rst-206-   the PCI LINK.\n--\ndrivers/nvme/target/pci-epf.c=79=struct nvmet_pci_epf_queue {\n--\ndrivers/nvme/target/pci-epf.c-88-\tsize_t\t\t\t\tpci_size;\ndrivers/nvme/target/pci-epf.c:89:\tstruct pci_epc_map\t\tpci_map;\ndrivers/nvme/target/pci-epf.c-90-\n--\ndrivers/nvme/target/pci-epf.c=198=struct nvmet_pci_epf {\n--\ndrivers/nvme/target/pci-epf.c-200-\ndrivers/nvme/target/pci-epf.c:201:\tconst struct pci_epc_features\t*epc_features;\ndrivers/nvme/target/pci-epf.c-202-\n--\ndrivers/nvme/target/pci-epf.c=254=static inline int nvmet_pci_epf_mem_map(struct nvmet_pci_epf *nvme_epf,\ndrivers/nvme/target/pci-epf.c:255:\t\tu64 pci_addr, size_t size, struct pci_epc_map *map)\ndrivers/nvme/target/pci-epf.c-256-{\n--\ndrivers/nvme/target/pci-epf.c-258-\ndrivers/nvme/target/pci-epf.c:259:\treturn pci_epc_mem_map(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-260-\t\t\t       pci_addr, size, map);\n--\ndrivers/nvme/target/pci-epf.c=263=static inline void nvmet_pci_epf_mem_unmap(struct nvmet_pci_epf *nvme_epf,\ndrivers/nvme/target/pci-epf.c:264:\t\t\t\t\t   struct pci_epc_map *map)\ndrivers/nvme/target/pci-epf.c-265-{\n--\ndrivers/nvme/target/pci-epf.c-267-\ndrivers/nvme/target/pci-epf.c:268:\tpci_epc_mem_unmap(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no, map);\ndrivers/nvme/target/pci-epf.c-269-}\n--\ndrivers/nvme/target/pci-epf.c=413=static int nvmet_pci_epf_mmio_transfer(struct nvmet_pci_epf *nvme_epf,\n--\ndrivers/nvme/target/pci-epf.c-418-\tvoid *buf = seg-\u003ebuf;\ndrivers/nvme/target/pci-epf.c:419:\tstruct pci_epc_map map;\ndrivers/nvme/target/pci-epf.c-420-\tint ret = -EINVAL;\n--\ndrivers/nvme/target/pci-epf.c=595=static void nvmet_pci_epf_raise_irq(struct nvmet_pci_epf_ctrl *ctrl,\n--\ndrivers/nvme/target/pci-epf.c-619-\t\t */\ndrivers/nvme/target/pci-epf.c:620:\t\tret = pci_epc_raise_irq(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-621-\t\t\t\t\tnvme_epf-\u003eirq_type, cq-\u003evector + 1);\n--\ndrivers/nvme/target/pci-epf.c-625-\tcase PCI_IRQ_INTX:\ndrivers/nvme/target/pci-epf.c:626:\t\tret = pci_epc_raise_irq(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-627-\t\t\t\t\tPCI_IRQ_INTX, 0);\n--\ndrivers/nvme/target/pci-epf.c=2133=static int nvmet_pci_epf_configure_bar(struct nvmet_pci_epf *nvme_epf)\n--\ndrivers/nvme/target/pci-epf.c-2135-\tstruct pci_epf *epf = nvme_epf-\u003eepf;\ndrivers/nvme/target/pci-epf.c:2136:\tconst struct pci_epc_features *epc_features = nvme_epf-\u003eepc_features;\ndrivers/nvme/target/pci-epf.c-2137-\tsize_t reg_size, reg_bar_size;\n--\ndrivers/nvme/target/pci-epf.c-2143-\t */\ndrivers/nvme/target/pci-epf.c:2144:\tif (pci_epc_get_first_free_bar(epc_features) != BAR_0) {\ndrivers/nvme/target/pci-epf.c-2145-\t\tdev_err(\u0026epf-\u003edev, \"BAR 0 is not free\\n\");\n--\ndrivers/nvme/target/pci-epf.c-2153-\t * type to 64-bit. In the rare case that the PCI EPC does not support\ndrivers/nvme/target/pci-epf.c:2154:\t * configuring BAR0 as 64-bit, the call to pci_epc_set_bar() will fail,\ndrivers/nvme/target/pci-epf.c-2155-\t * and we will return failure back to the user.\n--\ndrivers/nvme/target/pci-epf.c=2212=static void nvmet_pci_epf_clear_bar(struct nvmet_pci_epf *nvme_epf)\n--\ndrivers/nvme/target/pci-epf.c-2215-\ndrivers/nvme/target/pci-epf.c:2216:\tpci_epc_clear_bar(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-2217-\t\t\t  \u0026epf-\u003ebar[BAR_0]);\n--\ndrivers/nvme/target/pci-epf.c=2220=static int nvmet_pci_epf_init_irq(struct nvmet_pci_epf *nvme_epf)\ndrivers/nvme/target/pci-epf.c-2221-{\ndrivers/nvme/target/pci-epf.c:2222:\tconst struct pci_epc_features *epc_features = nvme_epf-\u003eepc_features;\ndrivers/nvme/target/pci-epf.c-2223-\tstruct pci_epf *epf = nvme_epf-\u003eepf;\n--\ndrivers/nvme/target/pci-epf.c-2227-\tif (epc_features-\u003emsix_capable \u0026\u0026 epf-\u003emsix_interrupts) {\ndrivers/nvme/target/pci-epf.c:2228:\t\tret = pci_epc_set_msix(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-2229-\t\t\t\t       epf-\u003emsix_interrupts, BAR_0,\n--\ndrivers/nvme/target/pci-epf.c-2242-\tif (epc_features-\u003emsi_capable \u0026\u0026 epf-\u003emsi_interrupts) {\ndrivers/nvme/target/pci-epf.c:2243:\t\tret = pci_epc_set_msi(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-2244-\t\t\t\t      epf-\u003emsi_interrupts);\n--\ndrivers/nvme/target/pci-epf.c=2263=static int nvmet_pci_epf_epc_init(struct pci_epf *epf)\n--\ndrivers/nvme/target/pci-epf.c-2265-\tstruct nvmet_pci_epf *nvme_epf = epf_get_drvdata(epf);\ndrivers/nvme/target/pci-epf.c:2266:\tconst struct pci_epc_features *epc_features = nvme_epf-\u003eepc_features;\ndrivers/nvme/target/pci-epf.c-2267-\tstruct nvmet_pci_epf_ctrl *ctrl = \u0026nvme_epf-\u003ectrl;\n--\ndrivers/nvme/target/pci-epf.c-2312-\tepf-\u003eheader-\u003esubsys_vendor_id = ctrl-\u003etctrl-\u003esubsys-\u003esubsys_vendor_id;\ndrivers/nvme/target/pci-epf.c:2313:\tret = pci_epc_write_header(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-2314-\t\t\t\t   epf-\u003eheader);\n--\ndrivers/nvme/target/pci-epf.c-2320-\ndrivers/nvme/target/pci-epf.c:2321:\tret = pci_epc_set_bar(epf-\u003eepc, epf-\u003efunc_no, epf-\u003evfunc_no,\ndrivers/nvme/target/pci-epf.c-2322-\t\t\t      \u0026epf-\u003ebar[BAR_0]);\n--\ndrivers/nvme/target/pci-epf.c=2369=static int nvmet_pci_epf_link_down(struct pci_epf *epf)\n--\ndrivers/nvme/target/pci-epf.c-2378-\ndrivers/nvme/target/pci-epf.c:2379:static const struct pci_epc_event_ops nvmet_pci_epf_event_ops = {\ndrivers/nvme/target/pci-epf.c-2380-\t.epc_init = nvmet_pci_epf_epc_init,\n--\ndrivers/nvme/target/pci-epf.c=2386=static int nvmet_pci_epf_bind(struct pci_epf *epf)\n--\ndrivers/nvme/target/pci-epf.c-2388-\tstruct nvmet_pci_epf *nvme_epf = epf_get_drvdata(epf);\ndrivers/nvme/target/pci-epf.c:2389:\tconst struct pci_epc_features *epc_features;\ndrivers/nvme/target/pci-epf.c-2390-\tstruct pci_epc *epc = epf-\u003eepc;\n--\ndrivers/nvme/target/pci-epf.c-2395-\ndrivers/nvme/target/pci-epf.c:2396:\tepc_features = pci_epc_get_features(epc, epf-\u003efunc_no, epf-\u003evfunc_no);\ndrivers/nvme/target/pci-epf.c-2397-\tif (!epc_features) {\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c=566=static int cdns_pcie_ep_start(struct pci_epc *epc)\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-615-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:616:static const struct pci_epc_features cdns_pcie_epc_vf_features = {\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-617-\t.msi_capable = true,\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-621-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:622:static const struct pci_epc_features cdns_pcie_epc_features = {\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-623-\t.msi_capable = true,\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-627-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:628:static const struct pci_epc_features*\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-629-cdns_pcie_ep_get_features(struct pci_epc *epc, u8 func_no, u8 vfunc_no)\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-636-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:637:static const struct pci_epc_ops cdns_pcie_epc_ops = {\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-638-\t.write_header\t= cdns_pcie_ep_write_header,\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c=653=void cdns_pcie_ep_disable(struct cdns_pcie_ep *ep)\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-658-\tcdns_pcie_debugfs_deinit(\u0026ep-\u003epcie);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:659:\tpci_epc_deinit_notify(epc);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:660:\tpci_epc_mem_free_addr(epc, ep-\u003eirq_phys_addr, ep-\u003eirq_cpu_addr,\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-661-\t\t\t      SZ_128K);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:662:\tpci_epc_mem_exit(epc);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-663-}\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c=666=int cdns_pcie_ep_setup(struct cdns_pcie_ep *ep)\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-704-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:705:\tepc = devm_pci_epc_create(dev, \u0026cdns_pcie_epc_ops);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-706-\tif (IS_ERR(epc)) {\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-739-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:740:\tret = pci_epc_mem_init(epc, pcie-\u003emem_res-\u003estart,\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-741-\t\t\t       resource_size(pcie-\u003emem_res), PAGE_SIZE);\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-746-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:747:\tep-\u003eirq_cpu_addr = pci_epc_mem_alloc_addr(epc, \u0026ep-\u003eirq_phys_addr,\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-748-\t\t\t\t\t\t  SZ_128K);\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-762-\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:763:\tpci_epc_init_notify(epc);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-764-\n--\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-769- free_epc_mem:\ndrivers/pci/controller/cadence/pcie-cadence-ep.c:770:\tpci_epc_mem_exit(epc);\ndrivers/pci/controller/cadence/pcie-cadence-ep.c-771-\n--\ndrivers/pci/controller/dwc/pci-dra7xx.c=403=static int dra7xx_pcie_raise_irq(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pci-dra7xx.c-422-\ndrivers/pci/controller/dwc/pci-dra7xx.c:423:static const struct pci_epc_features dra7xx_pcie_epc_features = {\ndrivers/pci/controller/dwc/pci-dra7xx.c-424-\tDWC_EPC_COMMON_FEATURES,\n--\ndrivers/pci/controller/dwc/pci-dra7xx.c-428-\ndrivers/pci/controller/dwc/pci-dra7xx.c:429:static const struct pci_epc_features*\ndrivers/pci/controller/dwc/pci-dra7xx.c-430-dra7xx_pcie_get_features(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pci-dra7xx.c=441=static int dra7xx_add_pcie_ep(struct dra7xx_pcie *dra7xx,\n--\ndrivers/pci/controller/dwc/pci-dra7xx.c-473-\ndrivers/pci/controller/dwc/pci-dra7xx.c:474:\tpci_epc_init_notify(ep-\u003eepc);\ndrivers/pci/controller/dwc/pci-dra7xx.c-475-\n--\ndrivers/pci/controller/dwc/pci-imx6.c=132=struct imx_pcie_drvdata {\n--\ndrivers/pci/controller/dwc/pci-imx6.c-141-\tconst u32 mode_mask[IMX_PCIE_MAX_INSTANCES];\ndrivers/pci/controller/dwc/pci-imx6.c:142:\tconst struct pci_epc_features *epc_features;\ndrivers/pci/controller/dwc/pci-imx6.c-143-\tint (*select_ref_clk_src)(struct imx_pcie *pcie);\n--\ndrivers/pci/controller/dwc/pci-imx6.c=1556=static int imx_pcie_ep_raise_irq(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pci-imx6.c-1575-\ndrivers/pci/controller/dwc/pci-imx6.c:1576:static const struct pci_epc_features imx8m_pcie_epc_features = {\ndrivers/pci/controller/dwc/pci-imx6.c-1577-\tDWC_EPC_COMMON_FEATURES,\n--\ndrivers/pci/controller/dwc/pci-imx6.c-1585-\ndrivers/pci/controller/dwc/pci-imx6.c:1586:static const struct pci_epc_features imx8q_pcie_epc_features = {\ndrivers/pci/controller/dwc/pci-imx6.c-1587-\tDWC_EPC_COMMON_FEATURES,\n--\ndrivers/pci/controller/dwc/pci-imx6.c-1606- */\ndrivers/pci/controller/dwc/pci-imx6.c:1607:static const struct pci_epc_features imx95_pcie_epc_features = {\ndrivers/pci/controller/dwc/pci-imx6.c-1608-\tDWC_EPC_COMMON_FEATURES,\n--\ndrivers/pci/controller/dwc/pci-imx6.c-1613-\ndrivers/pci/controller/dwc/pci-imx6.c:1614:static const struct pci_epc_features*\ndrivers/pci/controller/dwc/pci-imx6.c-1615-imx_pcie_ep_get_features(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pci-imx6.c=1628=static int imx_add_pcie_ep(struct imx_pcie *imx_pcie,\n--\ndrivers/pci/controller/dwc/pci-imx6.c-1659-\ndrivers/pci/controller/dwc/pci-imx6.c:1660:\tpci_epc_init_notify(ep-\u003eepc);\ndrivers/pci/controller/dwc/pci-imx6.c-1661-\n--\ndrivers/pci/controller/dwc/pci-keystone.c=910=static int ks_pcie_am654_raise_irq(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pci-keystone.c-933-\ndrivers/pci/controller/dwc/pci-keystone.c:934:static const struct pci_epc_features ks_pcie_am654_epc_features = {\ndrivers/pci/controller/dwc/pci-keystone.c-935-\tDWC_EPC_COMMON_FEATURES,\n--\ndrivers/pci/controller/dwc/pci-keystone.c-947-\t * what is behind these reserved BARs, see the definition of struct\ndrivers/pci/controller/dwc/pci-keystone.c:948:\t * pci_epc_bar_rsvd_region.\ndrivers/pci/controller/dwc/pci-keystone.c-949-\t */\n--\ndrivers/pci/controller/dwc/pci-keystone.c-958-\ndrivers/pci/controller/dwc/pci-keystone.c:959:static const struct pci_epc_features*\ndrivers/pci/controller/dwc/pci-keystone.c-960-ks_pcie_am654_get_features(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pci-keystone.c=1124=static int ks_pcie_probe(struct platform_device *pdev)\n--\ndrivers/pci/controller/dwc/pci-keystone.c-1320-\ndrivers/pci/controller/dwc/pci-keystone.c:1321:\t\tpci_epc_init_notify(pci-\u003eep.epc);\ndrivers/pci/controller/dwc/pci-keystone.c-1322-\n--\ndrivers/pci/controller/dwc/pci-layerscape-ep.c=43=struct ls_pcie_ep {\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-44-\tstruct dw_pcie\t\t\t*pci;\ndrivers/pci/controller/dwc/pci-layerscape-ep.c:45:\tstruct pci_epc_features\t\t*ls_epc;\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-46-\tconst struct ls_pcie_ep_drvdata *drvdata;\n--\ndrivers/pci/controller/dwc/pci-layerscape-ep.c=115=static int ls_pcie_ep_interrupt_init(struct ls_pcie_ep *pcie,\n--\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-140-\ndrivers/pci/controller/dwc/pci-layerscape-ep.c:141:static const struct pci_epc_features*\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-142-ls_pcie_ep_get_features(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pci-layerscape-ep.c=224=static int __init ls_pcie_ep_probe(struct platform_device *pdev)\n--\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-228-\tstruct ls_pcie_ep *pcie;\ndrivers/pci/controller/dwc/pci-layerscape-ep.c:229:\tstruct pci_epc_features *ls_epc;\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-230-\tstruct resource *dbi_base;\n--\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-284-\ndrivers/pci/controller/dwc/pci-layerscape-ep.c:285:\tpci_epc_init_notify(pci-\u003eep.epc);\ndrivers/pci/controller/dwc/pci-layerscape-ep.c-286-\n--\ndrivers/pci/controller/dwc/pcie-artpec6.c=351=static int artpec6_pcie_raise_irq(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pcie-artpec6.c-368-\ndrivers/pci/controller/dwc/pcie-artpec6.c:369:static const struct pci_epc_features artpec6_pcie_epc_features = {\ndrivers/pci/controller/dwc/pcie-artpec6.c-370-\tDWC_EPC_COMMON_FEATURES,\n--\ndrivers/pci/controller/dwc/pcie-artpec6.c-373-\ndrivers/pci/controller/dwc/pcie-artpec6.c:374:static const struct pci_epc_features *\ndrivers/pci/controller/dwc/pcie-artpec6.c-375-artpec6_pcie_get_features(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pcie-artpec6.c=386=static int artpec6_pcie_probe(struct platform_device *pdev)\n--\ndrivers/pci/controller/dwc/pcie-artpec6.c-463-\ndrivers/pci/controller/dwc/pcie-artpec6.c:464:\t\tpci_epc_init_notify(pci-\u003eep.epc);\ndrivers/pci/controller/dwc/pcie-artpec6.c-465-\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=396=static int dw_pcie_ep_set_bar_resizable(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-411-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:412:\tret = pci_epc_bar_size_to_rebar_cap(size, \u0026rebar_cap);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-413-\tif (ret)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=454=static int dw_pcie_ep_set_bar_programmable(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-477-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:478:static enum pci_epc_bar_type dw_pcie_ep_get_bar_type(struct dw_pcie_ep *ep,\ndrivers/pci/controller/dwc/pcie-designware-ep.c-479-\t\t\t\t\t\t     enum pci_barno bar)\ndrivers/pci/controller/dwc/pcie-designware-ep.c-480-{\ndrivers/pci/controller/dwc/pcie-designware-ep.c:481:\tconst struct pci_epc_features *epc_features;\ndrivers/pci/controller/dwc/pcie-designware-ep.c-482-\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=491=static int dw_pcie_ep_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-498-\tsize_t size = epf_bar-\u003esize;\ndrivers/pci/controller/dwc/pcie-designware-ep.c:499:\tenum pci_epc_bar_type bar_type;\ndrivers/pci/controller/dwc/pcie-designware-ep.c-500-\tint flags = epf_bar-\u003eflags;\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=801=static int dw_pcie_ep_start(struct pci_epc *epc)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-808-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:809:static const struct pci_epc_features*\ndrivers/pci/controller/dwc/pcie-designware-ep.c-810-dw_pcie_ep_get_features(struct pci_epc *epc, u8 func_no, u8 vfunc_no)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-819-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:820:static const struct pci_epc_bar_rsvd_region *\ndrivers/pci/controller/dwc/pcie-designware-ep.c-821-dw_pcie_ep_find_bar_rsvd_region(struct dw_pcie_ep *ep,\ndrivers/pci/controller/dwc/pcie-designware-ep.c:822:\t\t\t\tenum pci_epc_bar_rsvd_region_type type,\ndrivers/pci/controller/dwc/pcie-designware-ep.c-823-\t\t\t\tenum pci_barno *bar,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-825-{\ndrivers/pci/controller/dwc/pcie-designware-ep.c:826:\tconst struct pci_epc_features *features;\ndrivers/pci/controller/dwc/pcie-designware-ep.c:827:\tconst struct pci_epc_bar_desc *bar_desc;\ndrivers/pci/controller/dwc/pcie-designware-ep.c:828:\tconst struct pci_epc_bar_rsvd_region *r;\ndrivers/pci/controller/dwc/pcie-designware-ep.c-829-\tint i, j;\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=879=dw_pcie_ep_get_aux_resources(struct pci_epc *epc, u8 func_no, u8 vfunc_no,\ndrivers/pci/controller/dwc/pcie-designware-ep.c:880:\t\t\t     struct pci_epc_aux_resource *resources,\ndrivers/pci/controller/dwc/pcie-designware-ep.c-881-\t\t\t     int num_resources)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-884-\tstruct dw_pcie *pci = to_dw_pcie_from_ep(ep);\ndrivers/pci/controller/dwc/pcie-designware-ep.c:885:\tconst struct pci_epc_bar_rsvd_region *rsvd;\ndrivers/pci/controller/dwc/pcie-designware-ep.c-886-\tstruct dw_edma_chip *edma = \u0026pci-\u003eedma;\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-919-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:920:\tresources[0] = (struct pci_epc_aux_resource) {\ndrivers/pci/controller/dwc/pcie-designware-ep.c-921-\t\t.type = PCI_EPC_AUX_DOORBELL_MMIO,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-935-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:936:static const struct pci_epc_ops epc_ops = {\ndrivers/pci/controller/dwc/pcie-designware-ep.c-937-\t.write_header\t\t= dw_pcie_ep_write_header,\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1187=void dw_pcie_ep_deinit(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1192-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1193:\tpci_epc_mem_free_addr(epc, ep-\u003emsi_mem_phys, ep-\u003emsi_mem,\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1194-\t\t\t      epc-\u003emem-\u003ewindow.page_size);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1195-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1196:\tpci_epc_mem_exit(epc);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1197-}\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1200=static void dw_pcie_ep_init_rebar_registers(struct dw_pcie_ep *ep, u8 func_no)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1236-\t\t\tif (ep_func-\u003eepf_bar[bar])\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1237:\t\t\t\tpci_epc_bar_size_to_rebar_cap(ep_func-\u003eepf_bar[bar]-\u003esize, \u0026val);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1238-\t\t\telse\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1288=static void dw_pcie_ep_disable_bars(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1290-\tstruct dw_pcie *pci = to_dw_pcie_from_ep(ep);\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1291:\tenum pci_epc_bar_type bar_type;\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1292-\tenum pci_barno bar;\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1444=void dw_pcie_ep_linkup(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1447-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1448:\tpci_epc_linkup(epc);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1449-}\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1460=void dw_pcie_ep_linkdown(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1472-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1473:\tpci_epc_linkdown(epc);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1474-}\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c=1521=int dw_pcie_ep_init(struct dw_pcie_ep *ep)\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1532-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1533:\tepc = devm_pci_epc_create(dev, \u0026epc_ops);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1534-\tif (IS_ERR(epc)) {\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1551-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1552:\tret = pci_epc_mem_init(epc, ep-\u003ephys_base, ep-\u003eaddr_size,\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1553-\t\t\t       ep-\u003epage_size);\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1558-\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1559:\tep-\u003emsi_mem = pci_epc_mem_alloc_addr(epc, \u0026ep-\u003emsi_mem_phys,\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1560-\t\t\t\t\t     epc-\u003emem-\u003ewindow.page_size);\n--\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1569-err_exit_epc_mem:\ndrivers/pci/controller/dwc/pcie-designware-ep.c:1570:\tpci_epc_mem_exit(epc);\ndrivers/pci/controller/dwc/pcie-designware-ep.c-1571-\n--\ndrivers/pci/controller/dwc/pcie-designware-plat.c=33=static int dw_plat_pcie_ep_raise_irq(struct dw_pcie_ep *ep, u8 func_no,\n--\ndrivers/pci/controller/dwc/pcie-designware-plat.c-51-\n\n"
}

gemini-3.8-flash

null

null

							input: 46381
							output: 22
							thoughts: 845
						

**PCI Endpoint Framework and Reachability Analysis for Fuzzing**

Okay, so the initial context is about the PCI endpoint framework, which, as I understand it, means running Linux *on* the PCIe device itself – think of an embedded SoC acting as a PCIe device, not a host running QEMU. And this patch specifically lives on the host side, within `setup-bus.c`.

My primary concern right now is whether this `pci_do_resource_release_and_resize` function is even *reachable* in a typical fuzzing setup like GCE VMs or a QEMU x86_64 environment.  Let's circle back to the fuzzing guidelines; reachability is the *key* filter.  If the code can't execute in standard virtualized environments, it's a no-go for fuzzing, regardless of how intricate the logic or how many assertions are added.

The guidelines state that code is *not* worth fuzzing if it's "structurally unreachable hardware" – like vendor-specific PCIe switches or GPU drivers that require real hardware not emulated in standard QEMU.  Also, code related to driver teardown during physical hot-unplug or manual unbinding.  That's important.

The guidelines explicitly mention "Vendor-specific PCIe switches, SmartNICs, or GPU drivers (e.g., mlxsw, pds_core, qed, ionic, amdgpu)".  This is relevant.

So, who calls `pci_do_resource_release_and_resize`? Only the AMD GPU driver (`amdgpu`), the Intel discrete GPU drivers (specifically i915 and xe) for LMEM resizing, and the sysfs entry `/sys/bus/pci/devices/.../resourceN_resize`, which *only* exists if the device supports the PCIe Resizable BAR extended capability (`PCI_EXT_CAP_ID_REBAR` / `PCI_EXT_CAP_ID_VF_REBAR`).

And here's the crucial point: Can *any* virtual device in QEMU report `PCI_EXT_CAP_ID_REBAR`?  No. QEMU doesn't have any virtual devices that implement that capability.  What about GCE? Nope, GCE instances use virtio/gVNIC.

Therefore, `pci_do_resource_release_and_resize` requires *physical* hardware – specifically, physical GPUs, like AMD Radeon or Intel Arc, that support PCIe Resizable BAR. This is not emulated in standard QEMU nor is it available in GCE/QEMU, the standard fuzzing environments.

Now, let me quickly double-check: is there *any* software emulation or a testing framework within the Linux kernel that would allow me to interact with PCI rebar?  I'll grep for `PCI_EXT_CAP_ID_REBAR`, `pci_rebar`, `resource.*_resize`, or `pci_resize_resource` across all the tests and drivers.  I will also check KUnit for relevant PCI tests within `drivers/pci/tests/` or similar.  Because if there is a *mock* driver, that could change everything.

{
  "Dir": "drivers/pci"
}

{
  "Files": [
    "access.c",
    "ats.c",
    "bus.c",
    "devres.c",
    "doe.c",
    "ecam.c",
    "host-bridge.c",
    "ide.c",
    "iomap.c",
    "iov.c",
    "irq.c",
    "mmap.c",
    "npem.c",
    "of.c",
    "of_property.c",
    "p2pdma.c",
    "pci-acpi.c",
    "pci-bridge-emul.c",
    "pci-bridge-emul.h",
    "pci-driver.c",
    "pci-label.c",
    "pci-mid.c",
    "pci-pf-stub.c",
    "pci-stub.c",
    "pci-sysfs.c",
    "pci.c",
    "pci.h",
    "probe.c",
    "proc.c",
    "quirks.c",
    "rebar.c",
    "remove.c",
    "rom.c",
    "search.c",
    "setup-bus.c",
    "setup-cardbus.c",
    "setup-res.c",
    "slot.c",
    "syscall.c",
    "tph.c",
    "trace.c",
    "tsm.c",
    "vc.c",
    "vgaarb.c",
    "vpd.c",
    "xen-pcifront.c"
  ],
  "Subdirs": [
    "controller",
    "endpoint",
    "hotplug",
    "msi",
    "pcie",
    "pwrctrl",
    "switch"
  ]
}

gemini-3.8-flash

null

null

							input: 48331
							output: 205
							thoughts: 767
						

**REBAR Modification - Unfuzzable**

Okay, let's break this down systematically. My initial thought was to quickly check for any existing PCI device emulation within the kernel's drivers/pci directory that might handle REBAR. `pci-bridge-emul.c` is for a specific MVEBU/Aardvark bridge, and `pci-stub.c` and `pci-pf-stub.c` are for physical devices, neither of which are relevant here. I immediately ruled them out as REBAR emulators.

My next line of thinking involved QEMU command-line options and syzkaller. Does either provide a way to configure a PCIe switch or device with REBAR capabilities within a standard virtualized environment? Nope. Syzkaller doesn't seem to touch that configuration.

Alright, let's revisit the prompt's requirements, specifically those negative criteria. The goal here is to determine if we *can't* fuzz this patch. Section 1 states reachability is key: if the code doesn't execute in a standard virtualized environment, don't bother fuzzing. Section 2 further clarifies that structurally unreachable hardware, such as vendor-specific PCIe switches, SmartNICs, or GPU drivers *requiring physical ASICs*, are not targets for fuzzing. Also, code paths only reachable via physical device hot-unplug or architecture-specific code are not fuzzed.

The patch modifies `pci_do_resource_release_and_resize` in `drivers/pci/setup-bus.c`, which specifically deals with PCIe Resizable BAR reconfiguration. It's clear that this code is executed in two ways: (1) via GPU driver probe/initialization for discrete GPUs (like amdgpu, i915, or xe, again *physical* GPUs); or (2) by writing to the `resource<N>_resize` sysfs attribute, which is only present for devices that *report* PCIe Resizable BAR capability.

Here's the problem: neither QEMU nor GCE emulates PCI devices with Resizable BAR capabilities. The underlying hardware needed to trigger `pci_do_resource_release_and_resize()` simply doesn't exist in the standard virtualized environments. This code path is, therefore, structurally unreachable for fuzzing purposes.

To double-check my work, I quickly verified that the git diff only touches `pci_do_resource_release_and_resize()`. It's entirely isolated, so no other factors are involved.

The conclusion is clear: **WorthFuzzing: false**. No fuzzing will be done. **FocusSymbols: []** and **EnableConfigs: []** are also empty as the code path is unreachable. I'm going to pass a concise explanation as **Reasoning**: "Concise explanation of why the modified code is unreachable in standard virtualized environments (QEMU / GCE)."

Now, I'm going to quickly check the parameters one last time:

*   `WorthFuzzing`: false
*   `FocusSymbols`: \[ ]
*   `EnableConfigs`: \[ ]
*   `Reasoning`: Concise explanation of why the modified code is unreachable in standard virtualized environments (QEMU / GCE).

Finally, I will call `set-results`.

{
  "EnableConfigs": [],
  "FocusSymbols": [],
  "Reasoning": "The patch modifies pci_do_resource_release_and_resize() in drivers/pci/setup-bus.c, which handles PCIe Resizable BAR (REBAR) reconfiguration. This function is only invoked during probe of physical discrete GPUs (amdgpu, i915, xe) or via the sysfs resource\u003cN\u003e_resize attribute. The sysfs attribute and the underlying helper are only accessible for devices advertising the PCIe Resizable BAR extended capability (PCI_EXT_CAP_ID_REBAR or PCI_EXT_CAP_ID_VF_REBAR), which requires physical PCIe hardware (e.g., discrete GPUs) and is not implemented or emulated by any virtual device in standard virtualized fuzzing environments (QEMU / GCE). Consequently, the modified code is structurally unreachable for syzkaller.",
  "WorthFuzzing": false
}

{
  "EnableConfigs": null,
  "FocusSymbols": [],
  "Reasoning": "The patch modifies pci_do_resource_release_and_resize() in drivers/pci/setup-bus.c, which handles PCIe Resizable BAR (REBAR) reconfiguration. This function is only invoked during probe of physical discrete GPUs (amdgpu, i915, xe) or via the sysfs resource\u003cN\u003e_resize attribute. The sysfs attribute and the underlying helper are only accessible for devices advertising the PCIe Resizable BAR extended capability (PCI_EXT_CAP_ID_REBAR or PCI_EXT_CAP_ID_VF_REBAR), which requires physical PCIe hardware (e.g., discrete GPUs) and is not implemented or emulated by any virtual device in standard virtualized fuzzing environments (QEMU / GCE). Consequently, the modified code is structurally unreachable for syzkaller.",
  "WorthFuzzing": false
}

{
  "WorthFuzzing": false
}

null